[Clinical analysis of liver dysfunction induced by SHR-1210 alone or combined with apatinib and chemotherapy in patients with advanced esophageal squamous cell carcinoma]

Objective: To investigate the clinical characteristics of abnormal liver function in patients with advanced esophageal squamous carcinoma treated with programmed death-1 (PD-1) antibody SHR-1210 alone or in combination with apatinib and chemotherapy. Methods: Clinical data of 73 patients with esophageal squamous carcinoma from 2 prospective clinical studies conducted at the Cancer Hospital Chinese Academy of Medical Sciences from May 11, 2016, to November 19, 2019, were analyzed, and logistic regression analysis was used for the analysis of influencing factors. Results: Of the 73 patients, 35 had abnormal liver function. 13 of the 43 patients treated with PD-1 antibody monotherapy (PD-1 monotherapy group) had abnormal liver function, and the median time to first abnormal liver function was 55 days. Of the 30 patients treated with PD-1 antibody in combination with apatinib and chemotherapy (PD-1 combination group), 22 had abnormal liver function, and the median time to first abnormal liver function was 41 days. Of the 35 patients with abnormal liver function, 2 had clinical symptoms, including malaise and loss of appetite, and 1 had jaundice. 28 of the 35 patients with abnormal liver function returned to normal and 7 improved to grade 1, and none of the patients had serious life-threatening or fatal liver function abnormalities. Combination therapy was a risk factor for patients to develop abnormal liver function (P=0.007). Conclusions: Most of the liver function abnormalities that occur during treatment with PD-1 antibody SHR-1210 alone or in combination with apatinib and chemotherapy are mild, and liver function can return to normal or improve with symptomatic treatment. For patients who receive PD-1 antibody in combination with targeted therapy and chemotherapy and have a history of long-term previous smoking, alcohol consumption and hepatitis B virus infection, liver function should be monitored and actively managed in a timely manner.

[Fuyu Decoction improves ventricular remodeling in rats with heart failure by inhibiting AMPK/mTOR pathway-mediated autophagy]

OBJECTIVE

To investigate the effect of Fuyu Decoction on ventricular remodeling and its association with AMPK/mTOR pathway-mediated autophagy in rats with heart failure.

METHODS

Thirty male Wistar rat models of heart failure induced by ligation of the left anterior descending coronary artery were divided into model group, Fuyu Decoction treatment group, Fuyu Decoction treatment +AMPK agonist group (n=10), with another 10 rats receiving sham operation as the Sham group. After 8 weeks of drug intervention, the changes of ventricular function and ventricular remodeling indexs of the rats were assessed. TTC staining was used to detect the myocardial infarction area, and HE and Masson staining were used to observe the pathological changes in the myocardial tissue. Western blotting was performed to detect the protein expressions of p-AMPK, p-mTOR, LC3-II, Beclin1 and p62 in the myocardial tissue.

RESULTS

Compared with the sham-operated rats, the rat models of heart failure showed significantly increased left ventricular end-diastolic volume (LVEDV), left ventricular endsystolic volume (LVESV), and left ventricular mass index (LVMI) (P < 0.01), reduced left ventricular ejection fraction (LVEF), left ventricular fractional shortening (LVFS), and decreased spherical index (SI) were (P < 0.01). The rat models also showed increased myocardial infarction area, obvious myocardial pathologies and fibrosis, increased apoptosis rate of the cardiomyocytes, enhanced myocardial expressions of p-AMPK, LC3-II/LC3-I and Beclin1 (P < 0.01), and reduced expressions of p-mTOR and p62 (P < 0.01). Fuyu Decoction treatment significantly ameliorated these changes in the rat models (all P < 0.01), but its effects were obviously blocked by treatment with EX229.

CONCLUSION

Fuyu Decoction can improve ventricular remodeling in rats with heart failure by inhibiting AMPK/mTOR signaling-mediated autophagy in the cardiomyocytes.

Chinese expert consensus on the diagnosis and treatment of thymic epithelial tumors

Thymic epithelial tumors (TETs) are a relatively rare type of thoracic tumor, accounting for less than 1% of all tumors. The incidence of TETs is about 3.93/10000 in China, slightly higher than that of European and American countries. For resectable TETs, complete surgical resection is recommended. Radiotherapy or chemotherapy may be used as postoperative adjuvant treatment. Treatment for advanced, unresectable TETs consist mainly of radiotherapy and chemotherapy, but there is a lack of standard first- and second-line treatment regimens. Recently, targeted therapies and immune checkpoint inhibitors have shown promising outcomes in TETs. Based on the currently available clinical evidences and the opinions of the national experts, the Thymic Oncology Group of Yangtze River Delta Lung Cancer Cooperation Group (East China LUng caNcer Group, ECLUNG; Youth Committee) established this Chinese expert consensus on the clinical diagnosis and treatment of TETs, covering the epidemiology, diagnosis, treatment, prognosis and follow-up of TETs.

[Clinical and genetic characteristics of young patients with myeloproliferative neoplasms]

Objectives: To investigate the clinical and genetic features of young Chinese patients with myeloproliferative neoplasms (MPN). Methods: In this cross-sectional study, anonymous questionnaires were distributed to patients with MPN patients nationwide. The respondents were divided into 3 groups based on their age at diagnosis: young (≤40 years) , middle-aged (41-60 years) , and elderly (>60 years) . We compared the clinical and genetic characteristics of three groups of MPN patients. Results: 1727 assessable questionnaires were collected. There were 453 (26.2%) young respondents with MPNs, including 274 with essential thrombocythemia (ET) , 80 with polycythemia vera (PV) , and 99 with myelofibrosis. Among the young group, 178 (39.3%) were male, and the median age was 31 (18-40) years. In comparison to middle-aged and elderly respondents, young respondents with MPN were more likely to present with a higher proportion of unmarried status (all P<0.001) , a higher education level (all P<0.001) , less comorbidity (ies) , fewer medications (all P<0.001) , and low-risk stratification (all P<0.001) . Younger respondents experienced headache (ET, P<0.001; PV, P=0.007; MF, P=0.001) at diagnosis, had splenomegaly at diagnosis (PV, P<0.001) , and survey (ET, P=0.052; PV, P=0.063) . Younger respondents had fewer thrombotic events at diagnosis (ET, P<0.001; PV, P=0.011) and during the survey (ET, P<0.001; PV, P=0.003) . JAK2 mutations were found in fewer young people (ET, P<0.001; PV, P<0.001; MF, P=0.013) ; however, CALR mutations were found in more young people (ET, P<0.001; MF, P=0.015) . Furthermore, mutations in non-driver genes (ET, P=0.042; PV, P=0.043; MF, P=0.004) and high-molecular risk mutations (ET, P=0.024; PV, P=0.023; MF, P=0.001) were found in fewer young respondents. Conclusion: Compared with middle-aged and elderly patients, young patients with MPN had unique clinical and genetic characteristics.

Extreme eutrophication and salinisation in the Coorong estuarine-lagoon ecosystem of Australia's largest river basin (Murray-Darling)

Estuaries in rainfall poor regions are highly susceptible to climatic and hydrological changes. The Coorong, a Ramsar-listed estuarine-coastal lagoon at the end of the Murray-Darling Basin (Australia), has experienced declining ecological health over recent decades. Twenty years of environmental data were analysed to assess patterns and drivers of water quality changes. Large areas of the Coorong are now persistently hyper-saline (salinity >80 psu) and hypereutrophic (total nitrogen, TN > 4 mg L^-1, total phosphorus, TP > 0.2 mg L^-1, chlorophyll a > 50 μg L^-1) which coincided with reduced flushing due to diminished freshwater inflows and increasing evapo-concentration. Sediment quality also was related to flushing, with higher concentrations of organic carbon, TN, TP and sulfides as salinity increased. While total nutrient levels are very high, dissolved inorganic nutrients are generally low. Increased lagoonal flushing would be beneficial to reduce the hypersalinisation and hypereutrophication and improve ecosystem health.

Enhanced foliar 15 N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

Determining the abundance of N isotope (δ¹⁵ N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their ¹⁵ N signatures remains unclear. Here, the response of ¹⁵ N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH₄ HCO₃ , urea, and NH₄ NO₃ ) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ¹⁵ N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N₂ -fixing species) showed significantly lower ¹⁵ N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ¹⁵ N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m^-2  year^-1 . Foliar δ¹⁵ N values were significantly higher when NH₄ HCO₃ and urea were added than when NH₄ NO₃ was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.

In Silico Discovery of Small Molecule Modulators Targeting the Achilles' Heel of SARS-CoV-2 Spike Protein

The spike protein of SARS-CoV-2 has been a promising target for developing vaccines and therapeutics due to its crucial role in the viral entry process. Previously reported cryogenic electron microscopy (cryo-EM) structures have revealed that free fatty acids (FFA) bind with SARS-CoV-2 spike protein, stabilizing its closed conformation and reducing its interaction with the host cell target in vitro. Inspired by these, we utilized a structure-based virtual screening approach against the conserved FFA-binding pocket to identify small molecule modulators of SARS-CoV-2 spike protein, which helped us identify six hits with micromolar binding affinities. Further evaluation of their commercially available and synthesized analogs enabled us to discover a series of compounds with better binding affinities and solubilities. Notably, our identified compounds exhibited similar binding affinities against the spike proteins of the prototypic SARS-CoV-2 and a currently circulating Omicron BA.4 variant. Furthermore, the cryo-EM structure of the compound SPC-14 bound spike revealed that SPC-14 could shift the conformational equilibrium of the spike protein toward the closed conformation, which is human ACE2 (hACE2) inaccessible. Our identified small molecule modulators targeting the conserved FFA-binding pocket could serve as the starting point for the future development of broad-spectrum COVID-19 intervention treatments.

[Analysis of the difference in MGMT promoter status in gliomas and its significance in prognosis assessment]

The data of 1 268 newly diagnosed gliomas from the Fourth Ward of Neurosurgery Department of Beijing Tiantan Hospital between April 2013 and March 2022 were retrospectively analyzed. Based on postoperative pathology, the gliomas were divided into groups: oligodendrogliomas (n=308), astrocytomas (n=337) and glioblastomas (n=623). According to the O6-methylguanine-DNA methyl transferase (MGMT) promoter status defined by the 12% of best cut-off value in previous research results, patients were divided into methylation group (n=763) and non-methylation group (n=505). Methylation level [M (Q₁, Q₃)] in patients with glioblastoma, astrocytoma and oligodendroglioma was 6% (2%, 24%), 17% (10%, 28%) and 29% (19%, 40%), respectively (P<0.001). Compared with non-methylation patients, the progression-free survival (PFS) and overall survival (OS) of glioblastomas patients with methylation of MGMT promoter demonstrated more favorable prognosis [M (Q₁, Q₃)]) of PFS: 14.0 (6.0, 36.0) months vs 8.0 (4.0, 15.0) months, P<0.001; M (Q₁, Q₃) of OS: 29.0 (17.0, 60.5) months vs 16.0 (11.0, 26.5) months, P<0.001]. In astrocytomas patients, the PFS was much longer for those with methylation [the median PFS of patients with methylation was not observed at the end of follow-up, but those without methylation showed a median PFS of 46.0 (29.0, 52.0) months] (P=0.001). However, no statistically significant difference was observed in OS [the median OS of patients with methylation was not observed at the end of follow-up, but those without methylation had a median OS of 62.0 (46.0, 98.0) months] (P=0.085). In oligodendrogliomas patients, no statistically significant differences of PFS and OS were observed between patients with methylation and those without methylation. MGMT promoter status was a related factor affecting PFS and OS in glioblastomas (PFS: HR=0.534,95%CI: 0.426-0.668, P<0.001; OS: HR=0.451, 95%CI: 0.353-0.576, P<0.001). Moreover, MGMT promoter status was also a related factor affecting PFS in astrocytomas (HR=0.462, 95%CI: 0.221-0.966, P=0.040), but not for OS (HR=0.664, 95%CI: 0.259-1.690, P=0.389). The methylation level of MGMT promoter differed substantially in different types of gliomas, and the status of MGMT promoter profoundly affected the prognosis of glioblastomas.

[Combination of anlotinib and irinotecan in the second-line treatment of metastatic colorectal cancer: a multicenter phase 1/2 trial]

Objective: To evaluate the safety and efficacy of anlotinib plus irinotecan in the second-line treatment of patients with metastatic colorectal cancer (mCRC). Methods: This prospective phase 1/2 study was conducted in 2 centers in China (Cancer Hospital of Chinese Academy of Medical Sciences and Jiangsu Province Hospital). We enrolled patients with mCRC whose disease had progressed after first-line systemic therapy and had not previously treated with irinotecan to receive anlotinib plus irinotecan. In the phase 1 of the trial, patients received anlotinib (8 mg, 10 mg or 12 mg, po, 2 weeks on/1 week off) in combination with fixed-dose irinotecan (180 mg/m(2), iv, q2w) to define the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D). In the phase 2, patients were treated with the RP2D of anlotinib and irinotecan. The primary endpoints were MTD and objective response rate (ORR). Results: From May 2018 to January 2020, a total of 31 patients with mCRC were enrolled. Anlotinib was well tolerated in combination with irinotecan with no MTD identified in the phase 1, and the RP2D was 12 mg. Thirty patients were evaluable for efficacy analysis. Eight patients achieved partial response, and 21 had stable disease, 1 had progressive disease. The ORR was 25.8% and the disease control rate was 93.5%. With a median follow-up duration of 29.5 months, the median progression-free survival and overall survival were 6.9 months (95% CI: 3.7, 9.3) and 17.6 months (95% CI: 12.4, not evaluated), respectively. The most common grade 3 treatment-related adverse events (≥10%) were neutropenia (25.8%) and diarrhea (16.1%). There was no treatment-related death. Conclusion: The combination of anlotinib and irinotecan has promising anti-tumor activity in the second-line treatment of mCRC with a manageable safety profile.

[Fibrocartilaginous mesenchymoma: a clinicopathological analysis of four cases]

Objective: To investigate the clinical, radiological, histological and molecular features and the differential diagnosis of fibrocartilaginous mesenchymoma (FM). Methods: Four cases of FM diagnosed in the Department of Pathology, the Sixth People's Hospital Affiliated to Shanghai Jiaotong University School of Medicine from 2020 to 2022 were analyzed. Related literature was also reviewed. Results: Case 1 was a 10-year-old girl with bone destruction in the sacrum and L5 articular processes revealed by CT scan. Case 2 was a 7-year-old girl with an aggressive lesion in her right distal ulna. Case 3 was an 11-year-old boy with a lesion in the metaphysis of his left proximal tibia. Case 4 was an 11-year-old boy with bone destruction in the distal portion of a radius. Microscopically, the four tumors all consisted of numerous spindle cells, hyaline cartilage nodules, and bone trabeculae. The hypocellular to moderately cellular spindle cell component contained elongated cells with slightly hyperchromatic, mildly atypical nuclei arranged in bundles or intersecting fascicles. Benign-appearing cartilaginous nodules of various sizes and shapes were scattered throughout the tumors. There were areas mimicking epiphyseal growth-plate characterized by chondrocytes arranged in parallel columns and areas of enchondral ossification. The stroma was rich in mucus in case 1. Mutation of GNAS and IDH1/IDH2 and amplification of MDM2 gene were not found in any of the three tested cases. Conclusions: FM is very rare and tends to affect young patients. It most frequently occurs in the metaphysis of long tubular bones, followed by the iliac-pubic bones and vertebrae. FM is characterized by a mixed population of spindle cells, hyaline cartilage nodules and trabeculae of bone, without specific immunophenotypes and molecular alternations. As a borderline, locally aggressive neoplasm, surgical removal with a wide margin is generally the treatment of choice for FM.

Association between time of onset and Omicron BA.2 RNA clearance time in children: a retrospective cohort study

Background

The association between the time of onset [time from the date of detection of a positive real-time reverse-transcription polymerase chain reaction (RT-PCR) to the date of detection of a positive RT-PCR in the first child] and viral RNA clearance time (time from first positive RT-PCR to two consecutive negative RT-PCR) remains unclear. Our study aimed to evaluate their association. That can provide a reference for the number of nucleic acid tests.

Methods

We conducted a retrospective analysis of children diagnosed with Omicron BA.2 infection at Fujian Medical University Affiliated First Quanzhou Hospital between March 14, 2022 (date the first child in the outbreak was found positive for RT-PCR) and April 9, 2022 (date the last child was found positive for RT-PCR). We used the electronic medical record to extract demographic data, symptoms, radiology and laboratory findings, treatments, and viral RNA clearance time. The 282 children were divided equally into 3 groups according to the time of onset. We calculated the factors affecting viral RNA clearance time by univariate and multivariate analysis. We used the generalized additive model to investigate the relationship between the time of onset and viral RNA clearance time.

Results

46.45% of children were female. Fever (62.06%) and cough (15.60%) were the dominant onset symptoms. We found no serious cases and all children were cured. The median time to viral RNA clearance was 14 days (IQR 12-17 days), with a range of 5 to 35 days. After adjustment for potential confounders, the viral RNA clearance time was reduced by 2.45 (95% CI: 0.85, 4.04) days in the 7-10 days group and by 4.62 (95% CI: 2.38, 6.14) days in > 10 days group compared to the ≤6 days group. There was a non-linear association between the time of onset and viral RNA clearance time.

Conclusions

Time of onset was non-linearly associated with Omicron BA.2 RNA clearance time. During the first 10 days of the outbreak, viral RNA clearance time decreased with increasing onset date. After 10 days of the outbreak, viral RNA clearance time did not decrease with increasing onset date.

[Analysis on causes and influencing factors of sudden death on job of workers in a large oil field branch plant during 2014-2020]

Objective: To investigate the epidemiological characteristics of sudden death on job among workers in the large oil field, and to provide scientific basis for dealing with such incidents. Methods: In April 2021, the medical records of employees who died in a large oilfield from 2014 to 2020, and the occupational health examination data in the first year of life were collected, and 85 employees who died suddenly on duty were included in the study. According to whether the employees are exposed to the occupational disease hazards, they are divided into the injured type of work (66 persons) and the non injured type of work (19 persons) . The characteristics of the clinical data of the sudden death employees are analyzed retrospectively. The gender, age, length of service, type of work, distribution of causes of sudden death of the cases are analyzed. The detection of abnormalities in various occupational health examination indicators is analyzed. The chi square test is used to analyze the distribution of the types of work, length of service and abnormal physical examination indicators. Results: Among the 85 employees who died suddenly on duty, the ratio of men and women was 16∶1. The proportion of sudden death among employees aged 40 to 50 years was the highest (54.12%, 46/85) , which was mainly the first-line workers in the affected departments (43.53%, 37/85) and those with 20-30 years of service (57.64%, 49/85) . The main cause of sudden death was cardiogenic sudden death (78.82%, 67/85) . There were statistically significant differences in abnormal rates of blood pressure and blood glucose among workers of different types of work (χ(2)=7.24, 24.22, P<0.05) , and there were statistically significant differences in abnormal rates of blood lipid and blood glucose among workers of different ages of service (χ(2)=12.37, 31.44, P<0.05) Conclusion: Higher risks of sudden death on job are male, older than 40 years old, front-line workers in disaster receiving departments, worked for more than 30 years, and have abnormal cardiovascular indicators. Workers with these high risks are the major target population for the prevention and treatment of sudden death on the job. It's necessary to supervise enterprises to implement protective measures against risk factors, and to strengthen health education and reduce the incidence of cardiovascular and cerebrovascular diseases, in order to reduce the occurrence rate of sudden death in oilfield workers.

Pretreatment with propofol restores intestinal epithelial cells integrity disrupted by mast cell degranulation in vitro

Propofol has been shown to against intestinal reperfusion injury when treated either before or after ischemia, during which mast cell could be activated. The aim of this study was to evaluate the role of propofol in restoring the intestinal epithelial cells integrity disrupted by mast cell activation or the released tryptase after activation in vitro. We investigated the effect of: (1) tryptase on Caco-2 monolayers in the presence of PAR-2 inhibitor or propofol, (2) mast cell degranulation in a Caco-2/LAD-2 co-culture model in the presence of propofol, and (3) propofol on mast cell degranulation. Epithelial integrity was detected using transepithelial resistance (TER) and permeability to fluorescein isothiocyanate (FITC)-dextran (the apparent permeability coefficient, Papp). The expression of junctional proteins zonula occludens-1 (ZO-1/TJP1) and occludin were determined using western blot analysis and immunofluorescence microscopy. The intracellular levels of reactive oxidative species (ROS) and Ca2+ were measured using flow cytometry. Tryptase directly enhanced intestinal barrier permeability as demonstrated by significant reductions in TER, ZO-1, and occludin protein expression and concomitant increases in Papp. The intestinal barrier integrity was restored by PAR-2 inhibitor but not by propofol. Meanwhile, mast cell degranulation resulted in epithelial integrity disruption in the Caco-2/LAD-2 co-culture model, which was dramatically attenuated by propofol. Mast cell degranulation caused significant increases in intracellular ROS and Ca2+ levels, which were blocked by propofol and NAC. Propofol pretreatment can inhibit mast cell activation via ROS/Ca2+ and restore the intestinal barrier integrity induced by mast cell activation, instead of by tryptase.

Chinese expert consensus on the multidisciplinary management of pneumonitis associated with immune checkpoint inhibitor

Immune checkpoint inhibitors (ICIs) have successfully treated a number of different types of cancer, which is of great significance for cancer treatment. With the widespread use of ICIs in clinical practice, the increasing checkpoint inhibitor pneumonia (CIP) will be a challenge to clinicians. To guide the diagnosis and treatment of CIP, we conducted in-depth discussions based on the latest evidence, forming a consensus among Chinese experts on the multidisciplinary management of CIP.

Chinese expert consensus on the diagnosis and treatment of HER2-altered non-small cell lung cancer

Human epidermal growth factor receptor 2 (HER2) possesses tyrosine kinase activity and participates in cell growth, differentiation and migration, and survival. Its alterations, mainly including mutations, amplifications, and overexpression are associated with poor prognosis and are one of the major drivers in non-small cell lung cancer (NSCLC). Several clinical trials had been investigating on the treatments of HER2-altered NSCLC, including conventional chemotherapy, programmed death 1 (PD-1) inhibitors, tyrosine kinase inhibitors (TKIs) and antibody-drug conjugates (ADCs), however, the results were either disappointing or encouraging, but inconsistent. Trastuzumab deruxtecan (T-DXd) was recently approved by the Food and Drug Administration as the first targeted agent for treating HER2-mutant NSCLC. Effective screening of patients is the key to the clinical application of HER2-targeted agents such as TKIs and ADCs. Various testing methods are nowadays available, including polymerase chain reaction (PCR), next-generation sequencing (NGS), fluorescence in situ hybridization (FISH), immunohistochemistry (IHC), etc. Each method has its pros and cons and should be reasonably assigned to appropriate patients for diagnosis and guiding treatment decisions. To help standardize the clinical workflow, our expert group reached a consensus on the clinical management of HER2-altered NSCLC, focusing on the diagnosis and treatment strategies.

Positive legacies of severe droughts in the Inner Mongolia grassland

Global change-induced extreme droughts are increasing in grasslands worldwide, and drought legacies may greatly affect the responses of grassland ecosystems to these changes. However, it remains poorly understood whether and how severe droughts have a positive legacy effect on grassland productivity. By combining a 4-year precipitation manipulation experiment with a 40-year observational study in a semiarid grassland, we showed that extreme droughts could create strong positive legacies on community productivity and that such legacies could last for multiple years. The mechanism behind this was the coupled effect of the drought-induced increase in annuals and the favorable precipitation pattern that facilitated the flourishing of annuals in subsequent years. This study provides experimental and observational evidence for positive drought legacies and reveals their underlying mechanisms. Our findings suggest that positive drought legacies should be incorporated into Earth system models to better predict the impact of extreme droughts on grassland ecosystems.