# Trade-Offs of Plant Biomass by Precipitation Regulation Across the Sanjiangyuan Region of Qinghai–Tibet Plateau

## TL;DR

This study explores how rainfall affects plant biomass distribution in alpine grasslands on the Qinghai–Tibet Plateau, revealing that precipitation is a key driver of aboveground and belowground biomass trade-offs.

## Contribution

The study identifies precipitation as the dominant factor regulating biomass allocation in alpine grasslands, surpassing other variables like specific leaf area.

## Key findings

- Precipitation explained 31.71% of the variance in aboveground–belowground biomass trade-offs.
- Aboveground biomass growth accelerated under drier and wetter conditions, indicating preferential allocation to aboveground parts.
- Structural equation modeling confirmed precipitation's positive effects on aboveground and belowground biomass.

## Abstract

Climate change alters plant biomass allocation and aboveground–belowground trade-offs in grassland ecosystems, potentially affecting critical functions such as carbon sequestration. However, uncertainties persist regarding how precipitation gradients regulate (1) responses of aboveground biomass (AGB), belowground biomass (BGB), and total biomass in alpine grasslands, and (2) precipitation-mediated AGB-BGB allocation strategies. To address this, we conducted a large-scale field survey across precipitation gradients (400–700 mm/y) in the Sanjiangyuan alpine grasslands, Qinghai–Tibet Plateau. During the 2024 growing season, a total of 63 sites (including 189 plots and 945 quadrats) were sampled along five aridity classes: <400, 400–500, 500–600, 600–700, and >700 mm/y. Our findings revealed precipitation as the dominant driver of biomass dynamics: AGB exhibited equal growth rates relative to BGB within the 600–700 mm/y range, but accelerated under drier/wetter conditions. This suggests preferential allocation to aboveground parts under most precipitation regimes. Precipitation explained 31.71% of AGB–BGB trade-off variance (random forest IncMSE), surpassing contributions from AGB (17.61%), specific leaf area (SLA, 13.87%), and BGB (12.91%). Structural equation modeling confirmed precipitation’s positive effects on SLA (β = 0.28, p < 0.05), AGB (β = 0.53, p < 0.05), and BGB (β = 0.60, p < 0.05), with AGB-mediated cascades (β = 0.33, p < 0.05) dominating trade-off regulation. These results advance our understanding of mechanistic drivers governing allometric AGB–BGB relationships across climatic gradients in alpine ecosystems of the Sanjiangyuan Region on the Qinghai–Tibet Plateau.