Microbial nutrient limitations limit carbon sequestration but promote nitrogen and phosphorus cycling: A case study in an agroecosystem with long-term straw return

Straw return enhances grain yield and quality of three main crops: evidence from a meta-analysis

Straw return is regarded as a widely used field management strategy for improving soil health, but its comprehensive effect on crop grain yield and quality remains elusive. Herein, a meta-analysis containing 1822 pairs of observations from 78 studies was conducted to quantify the effect of straw return on grain yield and quality of three main crops (maize, rice, and wheat). On average, compared with no straw return, straw return significantly (p< 0.05) increased grain yield (+4.3%), protein content (+2.5%), total amino acids concentration (+1.2%), and grain phosphorus content (+3.6%), respectively. Meanwhile, straw return significantly (p< 0.05) decreased rice chalky grain rate (-14.4%), overall grain hardness (-1.9%), and water absorption of maize and wheat (-0.5%), respectively. Moreover, straw return effects on grain yield and quality traits were infected by cultivated crop types, straw return amounts, straw return methods, and straw return duration. Our findings illustrated that direct straw return increased three main crop grain yields and improved various quality traits among different agricultural production areas. Although improper straw return may increase plant disease risk and affect seed germination, our results suggest that full straw return with covered or plough mode is a more suitable way to enhance grain yield and quality. Our study also highlights that compared with direct straw return, straw burning or composting before application may also be beneficial to farmland productivity and sustainability, but comparative studies in this area are still lacking.

Stockpiling turf alters microbial carbon and nitrogen use efficiency on the Tibetan Plateau

Microbial carbon use efficiency (CUE) and nitrogen use efficiency (NUE) are crucial parameters reflecting soil C and N sequestration. Concerns about how artificial activities disturb alpine meadow ecosystem are increasing, but the knowledge of variances in microbial CUE and NUE in response to turf storage remains scarce. Here, we conducted a turf storage experiment on the Tibetan Plateau with two common storage methods, laying turfs method (LT) and stacking turfs method (ST). Plant litter, aboveground and belowground biomass declined considerably in the LT and ST than those in natural meadow. Soil pH and available phosphorus were significantly lower, but soil organic carbon, total nitrogen, dissolved organic carbon, and available nitrogen were substantially higher in stored turfs (both ST and LT) than in natural meadow. These results led to a differentiation in nutrient status among treatments. Vetor model indicated a stronger C limitation (vector length > 0.61) in ST than that in the LT and a shift from N to P limitation (vector angle >55°) in all stored turfs. Microbial CUE was prominently higher in the LT than those in the ST, signifying that microbes allocated more exogenous C to self-growth in the LT. Microbial NUE declined considerably in stored turfs, indicating a great proportion of N used for catabolic process instead of anabolic process. Microbial CUE and NUE were tightly linked to nutrient content and availability, enzymatic stoichiometry, microbial traits and plant biomass. Our results suggest that variations in microbial CUE and NUE were indirectly regulated by soil physicochemical properties via mediating nutrient imbalance and enzymatic stoichiometry in stored turfs.

Microplastics induced the differential responses of microbial-driven soil carbon and nitrogen cycles under warming

The input of microplastics (MPs) and warming interfere with soil carbon (C) or nitrogen (N) cycles. Although the effects of warming and/or MPs on the cycles have been well studied, the biological coupling of microbial-driven cycles was neglected. Here, the synergistic changes of the cycles were investigated using batch incubation experiments. As results, the influences of MPs were not significant at 15, 20, and 25 °C, and yet, high temperature (i.e., 30 °C) reduced the respiration of high-concentration MPs-amended soil by 9.80%, and increased dissolved organic carbon (DOC) by 14.74%. In contrast, high temperature did not change the effect of MPs on N. The decrease of microbial biomass carbon (MBC) and the constant of microbial biomass nitrogen (MBN) indicated that microbial N utilization was enhanced, which might be attributed to the enrichments of adapted populations, such as Conexibacter, Acidothermus, and Acidibacter. These observations revealed that high temperature and MPs drove the differential response of soil C and N cycles. Additionally, the transcriptomic provided genomic evidence of the response. In summary, the high temperature was a prerequisite for the MPs-driven response, which underscored new ecological risks of MPs under global warming and emphasized the need for carbon emission reduction and better plastic product regulation.