Leaf size (i.e., leaf surface area and leaf dry mass) profoundly affects a variety of biological carbon, water and energy processes. Therefore, the remarkable variability in individual leaf size and its trade-off with total leaf number in a plant have particularly important implications for understanding the adaption strategy of plants to environmental changes. The various leaf sizes of plants growing in the same habitat are expected to have distinct abilities of thermal regulation influencing leaf water loss and shedding heat. Here, we sampled 16 tree species co-occurring in a temperate forest in northeastern China to quantify the variation of leaf, stomata and twigs traits, and to determine the relationships of leaf size with leaf number and leaf water loss. We examined the right-skewed distributions of leaf size, leafing intensity, stomatal size and stomatal density across species. Leafing intensity was significantly negatively correlated with leaf size, accounting for 4 and 12% of variation in leaf area and leaf mass, respectively. Species was the most important factor in explaining the variation in leaf size (conditional R2 of 0.92 for leaf area and 0.82 for leaf mass). Leaf area and mass significantly increased with increasing diameter of twigs. Leaf water loss was strongly negatively correlated with leaf area and leaf mass during the first four hours of the measurement. Leaf area and leaf mass accounted for 38 and 30% of variation in total leaf water loss, respectively. Leaf water loss rate (k) was significantly different among tree species and markedly linearly decreased with increasing leaf area and leaf mass for simple-leaved tree species. In conclusion, the existence of a cross-species trade-off between the size of individual leaves and the number of leaves per yearly twig unit was confirmed in that temperate forest. There was strongly negative correlation between leaf water loss and leaf size across tree species, which provides evidences for leaf size in leaf temperature regulation in dry environment with strong radiation. The size-dependent leaf water relation is of central importance to recognize the functional role of leaf size in a changing climate including rapid changes in air temperature and rainfall.

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Fine root (≤2 mm in diameter) biomass/necromass (B/N) ratio, representing many dynamic key root parameters, can serve as a powerful measure of root vitality. Based on a global synthesis of fine root biomass and necromass in forest ecosystems, we describe a framework for recognizing responses of B/N ratio to biotic (e.g., mycorrhizal type) and abiotic (e.g., latitudinal region) characteristics. Arbuscular mycorrhiza (AM) and ectomycorrhiza (ECM) forests had similar average B/N ratios (3.28 versus 3.23). AM forest B/N ratio decreased with increasing altitude, stand density, tree age, and soil carbon/nitrogen ratio (C/N) but increased with soil pH. In contrast, ECM forest B/N ratio increased with increasing mean annual precipitation (MAP), altitude, and stand density but decreased with tree age. The average B/N ratio was higher in temperate forests (4.39) than in tropical (2.97) and boreal forests (2.40). The B/N ratio was relatively stable in temperate forests irrespective of changes in biotic and abiotic factors. In tropical forest, the B/N ratio was sensitive to mean annual temperature, altitude, soil C/N ratio, and pH, whereas in boreal forests, it was more sensitive to MAP, stand density, and tree age. The late‐successional forest B/N ratio was closely aligned with biotic and abiotic factors. Our analysis revealed that the relationships of B/N ratio with climate, topography, edaphic, and stand characteristics were dependent on mycorrhizal types and latitudinal regions. These findings provide a basis for large‐scale prediction of fine root dynamics and for better understanding of belowground processes of global forest ecosystems in a changing world.

Rice undergoes leaf senescence accompanied with grain filling when the plants reach the end of their temporal niche, and a delay in leaf senescence ultimately improves the yield and quality of grain. To estimate the decline in photosynthesis during leaf senescence and to find an efficient and useful tool to identify rice genotypes with a longer duration of active photosynthesis, we examined PSII photosynthetic activity in the flag leaves of japonica rice Shennong265 (SN265) and Beigeng3 (BG3) during leaf senescence using chlorophyll a fluorescence kinetics. The results show that inhibition occurred in the electron transport chains, but the energetic connectivity of PSII units was not affected as dramatically during leaf senescence. PSII reaction centres (RCs) were transformed into ‘silent RCs,’ and the chlorophyll content decreased during leaf senescence. However the size of the ‘economic’ antennae increased. Further, the percentage of variation of the specific energy flux parameters can rationally be used to indicate leaf senescence from the perspective of energy balance. Although the performance indices were more sensitive than other functional and structural JIP-test parameters, they still did not serve as an indicator of crop yield.