Unveiling the transferability of PLSR models for leaf trait estimation: lessons from a comprehensive analysis with a novel global dataset

Leaf traits are essential for understanding many physiological and ecological processes. Partial least squares regression (PLSR) models with leaf spectroscopy are widely applied for trait estimation, but their transferability across space, time, and plant functional types (PFTs) remains unclear. We compiled a novel dataset of paired leaf traits and spectra, with 47 393 records for > 700 species and eight PFTs at 101 globally distributed locations across multiple seasons. Using this dataset, we conducted an unprecedented comprehensive analysis to assess the transferability of PLSR models in estimating leaf traits. While PLSR models demonstrate commendable performance in predicting chlorophyll content, carotenoid, leaf water, and leaf mass per area prediction within their training data space, their efficacy diminishes when extrapolating to new contexts. Specifically, extrapolating to locations, seasons, and PFTs beyond the training data leads to reduced R2 (0.12-0.49, 0.15-0.42, and 0.25-0.56) and increased NRMSE (3.58-18.24%, 6.27-11.55%, and 7.0-33.12%) compared with nonspatial random cross-validation. The results underscore the importance of incorporating greater spectral diversity in model training to boost its transferability. These findings highlight potential errors in estimating leaf traits across large spatial domains, diverse PFTs, and time due to biased validation schemes, and provide guidance for future field sampling strategies and remote sensing applications.

Anatomical patterns of condensed tannin in fine roots of tree species from a cool-temperate forest

BACKGROUND AND AIMS

Condensed tannin (CT) is an important compound in plant biological structural defence and for tolerance of herbivory and environmental stress. However, little is known of the role and location of CT within the fine roots of woody plants. To understand the role of CT in fine roots across diverse species of woody dicot, we evaluated the localization of CT that accumulated in root tissue, and examined its relationships with the stele and cortex tissue in cross-sections of roots in 20 tree species forming different microbial symbiotic groups (ectomycorrhiza and arbuscular mycorrhiza).

METHODS

In a cool-temperate forest in Japan, cross-sections of sampled roots in different branching order classes, namely, first order, second to third order, fourth order, and higher than fourth order (higher order), were measured in terms of the length-based ratios of stele diameter and cortex thickness to root diameter. All root samples were then stained with ρ-dimethylaminocinnamaldehyde solution and we determined the ratio of localized CT accumulation area to the root cross-section area (CT ratio).

KEY RESULTS

Stele ratio tended to increase with increasing root order, whereas cortex ratio either remained unchanged or decreased with increasing order in all species. The CT ratio was significantly positively correlated to the stele ratio and negatively correlated to the cortex ratio in second- to fourth-order roots across species during the shift from primary to secondary root growth. Ectomycorrhiza-associated species mostly had a higher stele ratio and lower cortex ratio than arbuscular mycorrhiza-associated species across root orders. Compared with arbuscular mycorrhiza species, there was greater accumulation of CT in response to changes in the root order of ectomycorrhiza species.

CONCLUSIONS

Different development patterns of the stele, cortex and CT accumulation along the transition from root tip to secondary roots could be distinguished between different mycorrhizal associations. The CT in tissues in different mycorrhizal associations could help with root protection in specific branching orders during shifts in stele and cortex development before and during cork layer formation.

Five-year nitrogen addition affects fine root exudation and its correlation with root respiration in a dominant species, Quercus crispula, of a cool temperate forest, Japan

In forest ecosystems, fine root respiration directly contributes to belowground carbon (C) cycling. Exudation from fine roots indirectly affects C cycling via enhanced microbial decomposition of soil organic matter. Although these root-derived C fluxes are essential components of belowground C cycling, how nitrogen (N) addition affects these fluxes and their correlations remains unclear. In this study, fine root exudation, respiration and chemical/morphological traits were measured in a dominant canopy species, Quercus crispula Blume, found in a cool temperate forest, the Tomakomai Experimental Forest, Hokkaido University, which has undergone 5-year N addition. Soil-dissolved organic carbon (DOC) was also measured in both bulk and rhizosphere soils to evaluate the impact of fine root exudation on soil C cycling. Compared with a control plot with no N treatment, fine roots in the N addition plot exhibited larger diameters and higher N concentrations, but lower specific root lengths and areas. On a root-weight basis, respiration was not different between plots, but exudation was slightly higher under N addition. On a root-area basis, exudation was significantly higher in the N addition plot. Additionally, differences in DOC between rhizosphere and bulk soils were two times higher in the N addition plot than the control plot. Although fine root respiration was positively correlated with exudation in both the control and N addition plots, the ratio of exudation C to respiration C decreased after 5-year N addition. Nitrogen addition also affected absolute C allocation to fine root exudation and changed the C allocation strategy between exudation and respiration fluxes. These findings will help enhance predictions of belowground C allocation and C cycling under N-rich conditions in the future.

Quantitative assessment of plant-arthropod interactions in forest canopies: A plot-based approach

Research on canopy arthropods has progressed from species inventories to the study of their interactions and networks, enhancing our understanding of how hyper-diverse communities are maintained. Previous studies often focused on sampling individual tree species, individual trees or their parts. We argue that such selective sampling is not ideal when analyzing interaction network structure, and may lead to erroneous conclusions. We developed practical and reproducible sampling guidelines for the plot-based analysis of arthropod interaction networks in forest canopies. Our sampling protocol focused on insect herbivores (leaf-chewing insect larvae, miners and gallers) and non-flying invertebrate predators (spiders and ants). We quantitatively sampled the focal arthropods from felled trees, or from trees accessed by canopy cranes or cherry pickers in 53 0.1 ha forest plots in five biogeographic regions, comprising 6,280 trees in total. All three methods required a similar sampling effort and provided good foliage accessibility. Furthermore, we compared interaction networks derived from plot-based data to interaction networks derived from simulated non-plot-based data focusing either on common tree species or a representative selection of tree families. All types of non-plot-based data showed highly biased network structure towards higher connectance, higher web asymmetry, and higher nestedness temperature when compared with plot-based data. Furthermore, some types of non-plot-based data showed biased diversity of the associated herbivore species and specificity of their interactions. Plot-based sampling thus appears to be the most rigorous approach for reconstructing realistic, quantitative plant-arthropod interaction networks that are comparable across sites and regions. Studies of plant interactions have greatly benefited from a plot-based approach and we argue that studies of arthropod interactions would benefit in the same way. We conclude that plot-based studies on canopy arthropods would yield important insights into the processes of interaction network assembly and dynamics, which could be maximised via a coordinated network of plot-based study sites.

Effects of seasonal change and experimental warming on the temperature dependence of photosynthesis in the canopy leaves of Quercus serrata

The effects of warming on the temperature response of leaf photosynthesis have become an area of major concern in recent decades. Although growth temperature (GT) and day length (DL) affect leaf gas exchange characteristics, the way in which these factors influence the temperature dependence of photosynthesis remains uncertain. We established open-top canopy chambers at the canopy top of a deciduous forest, in which average daytime leaf temperature was increased by 1.0 °C. We conducted gas exchange measurements for the canopy leaves of deciduous trees exposed to artificial warming during different seasons. The carbon dioxide assimilation rate at 20 °C (A₂₀) was not affected by warming, whereas that at 25 °C (A₂₅) tended to be higher in leaves exposed to warming. Warming increased the optimal temperature of photosynthesis by increasing the activation energy for the maximum rate of carboxylation. Regression analysis indicated that both GT and DL strongly influenced gas exchange characteristics. Sensitivity analysis revealed that DL affected A without obvious effects on the temperature dependence of A, whereas GT almost maintained constant A₂₀ and strongly influenced the temperature dependence. These results indicate that GT and DL have different influences on photosynthesis; GT and DL affect the 'slope' and intercept' of the temperature dependence of photosynthesis, respectively.

Disruption of a gene encoding C4-dicarboxylate transporter-like protein increases ozone sensitivity through deregulation of the stomatal response in Arabidopsis thaliana

To understand better the plant response to ozone, we isolated and characterized an ozone-sensitive (ozs1) mutant strain from a set of T-DNA-tagged Arabidopsis thaliana ecotype Columbia. The mutant plants show enhanced sensitivity to ozone, desiccation and sulfur dioxide, but have normal sensitivity to hydrogen peroxide, low temperature and high light levels. The T-DNA was inserted at a single locus which is linked to ozone sensitivity. Identification of the genomic sequences flanking the T-DNA insertion revealed disruption of a gene encoding a transporter-like protein of the tellurite resistance/C(4)-dicarboxylate transporter family. Plants with either of two different T-DNA insertions in this gene were also sensitive to ozone, and these plants failed to complement ozs1. Transpiration levels, stomatal conductance levels and the size of stomatal apertures were greater in ozs1 mutant plants than in the wild type. The stomatal apertures of ozs1 mutant plants responded to light fluctuations but were always larger than those of the wild-type plants under the same conditions. The stomata of the mutant and wild-type plants responded similarly to stimuli such as light, abscisic acid, high concentrations of carbon dioxide and ozone. These results suggest that OZS1 helps to close stomata, being not involved in the responses to these signals.

A new member of the GTPase superfamily that is upregulated in highly metastatic cells

Two sublines of B16 melanoma cells, F10 and BL6, are metastatic after intravenous injection, but only BL6 cells are metastatic after subcutaneous injection. We found a new member of the GTPase superfamily, namely TIB929, which displayed an induction of expression in BL6 cells. It conserved three consensus sequences for GTP-binding site motifs and showed a significant homology to the yeast Gtr2 gene throughout the coding sequence. TIB929 was expressed ubiquitously in human tumor cells, with a marked expression in highly metastatic cells. TIB929 was mapped on mouse chromosome 4D, syntenic to human chromosome 1p. The results suggested an involvement of TIB929 in malignant progression.

[Late coronary artery aneurysm formation following directional coronary atherectomy]

The most important factor to reduce late restenosis following directional coronary atherectomy is the technical provision of the largest luminal diameter as possible. However, the safety of deep arterial resection and the resulting arterial perforation or late aneurysm formation is questionable. This study examined the frequency of coronary artery aneurysm formation in patients treated by directional coronary atherectomy. Ninety-eight patients with 123 lesions were analyzed by quantitative angiographic and histologic data. Coronary aneurysms (ratio of dilated vessel segment to the adjacent reference segment > 1.2:1) occurred in seven patients (seven lesions: 5.7%). Specimens were categorized by the deepest layer retrieved. Forty lesions (32.5%) were treated by resection of the intima alone, 65 (52.8%) by resection of the medial tissues and 18 (14.6%) received resections of the adventitial tissues including fatty tissues in three lesions. Late coronary aneurysms occurred often in lesions with resection of adventitial tissue (38.9%) and occurred in all three lesions with resections of fatty tissues. Six coronary aneurysms occurred in the left anterior descending artery (six in segs. 6, 7), and one aneurysm in the left circumflex artery. Among the target lesions in which coronary artery aneurysms were formed, six lesions were primary lesions and one lesion was a restenotic lesion after percutaneous transluminal coronary angioplasty. Statistically, patients with coronary artery aneurysms frequently have associated hypertension (p = 0.02) but rarely diabetes mellitus (p = 0.05). Lesions with late aneurysms had significantly high specimen weight (p = 0.01) and a trend to lower postprocedure % diameter (p = 0.20). There was no significant preprocedural angiographic predictor of aneurysms such as minimal lumen diameter or reference vessel diameter.

Detection of pyrimidine 5'-nucleotidase deficiency using 1H- or 31P-nuclear magnetic resonance

We describe here a further Japanese family with pyrimidine 5'-nucleotidase (P5'N) deficiency diagnosed using a nuclear magnetic resonance (NMR) spectrum, in Kumamoto prefecture where two families having the disease have been reported before. The specific spectra in 1H-NMR of P5'N deficient erythrocytes were due to three methyl protons of CDP-choline at 3.22 ppm and to H-2, H-8 and ribose-1' of pyrimidine nucleotide phosphate(s) in the lower fields (at 5.82 and 8.00 ppm). The other specificities in 31P-NMR spectra were due to CDP-choline, CDP-ethanolamine and UDP-glucose. Those spectra were not detected in other types of hemolytic anemia.

Immunologic studies on Werner's syndrome

Five patients with Werner's syndrome were studied to elucidate the relationship between the immune system and the ageing process. Three of five patients had neoplasms such as fibrosarcoma, meningioma and thyroid adenoma but none of the five patients manifested symptoms and signs suggestive of typical autoimmune disorders. Most immunohaematological data were normal; however, two patients exhibited diminished lymphocyte functions such as a significant (P less than 0 . 05) reduction in pokeweed mitogen (PWM) induced B cell differentiation, a slightly decreased response to Con A- or mitomycin-treated allogeneic lymphocytes and naturally occurring serum antibody to T cells. While these immunological changes were quantitatively small, subnormal levels of immune functions were detected. Cultured fibroblasts exhibited a decrease in clonal growth potentials and elongation of newly synthesized DNA, a decreased expression of HLA antigens, and a diminished secretion of beta 2-microglobulin.