Global drivers of plant leaf area on the branches

A recent research paper published in Plant, Cell & Environment describes the global variability in plant leaf area to sapwood area ratio in relation to climate, soil factors, tree density, biomes, plant functional types, and vegetation productivity.

A global greening trend has been observed, characterized by an increasing leaf area index (LAI), a longer growing season, and greater photosynthetic activity owing to CO₂ fertilization effects, nitrogen deposition, and climate change. Leaf area on branches, a direct factor influencing whole plant carbon gain and tree greening, is critical for plant light interception, transpiration, and growth, and varies largely across species.

Leaf area to sapwood area ratio (A_L/A_S, m² cm^-2), a useful trait to quantify plant leaves on branches, can be understood as the ratio of sum leaf area to a conductive xylem area of the branch. A_L/A_S is a key parameter for understanding plant-water relationships and photosynthesis. Accurately predicting A_L/A_S is helpful to a better understanding of community productivity, ecosystem function, and species distribution. However, critical predictors of A_L/A_S are not well understood.

A research group led by Professor YE Qing at South China Botanical Garden (SCBG) of Chinese Academy of Sciences (CAS) compiled an A_L/A_S dataset with 1612 species-at-site combinations (1137 woody species from 285 sites worldwide), and investigated the global patterns and drivers of A_L/A_S. They found that the global mean A_L/A_S to be 0.63 m² cm^-2, with its variation largely driven by growing-season precipitation. Species in tropical rainforests exhibited the highest A_L/A_S, whereas desert species showed the lowest value. Soil factors such as soil nitrogen and soil organic carbon exhibited positive effects on A_L/A_S, whereas soil pH was negatively correlated with A_L/A_S. Tree density accounted for 7% of the variation in A_L/A_S. All biotic and abiotic predictors collectively explained up to 45% of the variation in A_L/A_S. Additionally, A_L/A_S was positively correlated to the net primary productivity of the ecosystem.

“Given that growing-season precipitation is a critical driver of leaf area to sapwood area ratio, alterations in global precipitation belts, particularly seasonal precipitation, may induce changes in plant leaf area on the branches, potentially resulting in shifts in vegetation productivity across various biomes.” said Dr. HE Pengcheng, the first author of the paper.

For further reading, please find the paper entitled “Growing‐Season Precipitation Is a Key Driver of Plant Leaf Area to Sapwood Area Ratio at the Global Scale” at http://doi.org/10.1111/pce.15169.

Figure 1. Conceptual framework for water fluxes per unit leaf area on branches of plants under different water availability scenarios. Species may refer to the water availability that species are selected for, where more water-consuming species are assumed to be selected for wetter sites than are more drought-tolerant species at dry sites. The high leaf transpiration and carbon gain of water-consuming species require larger functional vessel size to maintain high hydraulic conductivity in the branches than is necessary for drought-tolerant species at dry sites. The difference in tree density at different sites also shapes leaf area on branches. Blue arrows and columns represent water fluxes and vessel size, respectively.