Effect of changing precipitation in different periods on precipitation use efficiency in a semi-arid grassland

Climate change intensifies global and regional water cycles, leading to
changes in both the magnitude and timing of precipitation. Precipitation
use efficiency (PUE) plays a crucial role in measuring the response of
above-ground net primary productivity (ANPP) to precipitation changes.
However, little is known about how changes in precipitation during
different periods affect PUE. Using a manipulation precipitation
experiment in a semi-arid steppe, we simulated a 60% increase and decrease
in precipitation during the early (April-June), late (July-September), and
entire (April-September) growing seasons across 2015-2021 to examine the
effects of changes in precipitation timing on PUE. The results showed
that: (1) decreased precipitation in the late growing season (DLP) and
whole growing season (DWP) stimulated PUE by an average of 0.14 and 0.12 g
m-2 mm-1 yr-1, respectively, whereas increased precipitation in the late
growing season (ILP) and whole growing season (IWP) suppressed PUE by an
average of 0.11 and 0.09g m-2 mm-1 yr-1, respectively. By contrast,
neither decreased nor increased precipitation in the early growing season
affected PUE; (2) the increased PUE under DLP was primarily attributed to
the increase of PUE in grass (GR) and annuals and biennials (AB), whereas
the elevation of PUE under DWP was mainly due to an increase of PUE in AB.
By contrast, the reduction of PUE under ILP was mainly caused by a decline
of PUE in GR; (3) changes in evapotranspiration and leaf dry matter
content (LDMC) explained the variation of PUE in AB while changes of PUE
in GR was mainly due to the alteration of soil water content and LDMC.
These results suggest that precipitation during the late growing season
has a crucial influence on PUE, highlighting the importance of
evapotranspiration and leaf dry matter content in regulating ecosystem
productivity in the semi-arid steppe.

气候变化加剧了全球及区域水循环，导致降水的强度和时间分布发生改变。降水利用效率（Precipitation Use Efficiency, PUE）在衡量地上净初级生产力（Above-ground Net Primary Productivity, ANPP）对降水变化的响应方面发挥着关键作用。然而，目前关于不同时期降水变化如何影响PUE的研究仍较为有限。通过在半干旱草原开展降水控制实验，我们在2015-2021年间模拟了生长季早期（4-6月）、晚期（7-9月）及整个生长季（4-9月）降水增加或减少60%的情景，以探究降水时间变化对PUE的影响。结果表明：（1）生长季晚期降水减少（DLP）和全生长季降水减少（DWP）分别使PUE平均提高0.14和0.12 g m⁻² mm⁻¹ yr⁻¹，而生长季晚期降水增加（ILP）和全生长季降水增加（IWP）则分别使PUE平均降低0.11和0.09 g m⁻² mm⁻¹ yr⁻¹；相比之下，生长季早期降水的增减均未对PUE产生显著影响；（2）DLP处理下PUE的提高主要归因于草本植物（GR）和一年生及二年生植物（AB）PUE的增加，而DWP处理下PUE的升高则主要源于AB的PUE提升；相反，ILP处理下PUE的降低主要由GR的PUE下降所致；（3）蒸散量和叶片干物质含量（Leaf Dry Matter Content, LDMC）的变化解释了AB的PUE变异，而GR的PUE变化主要由土壤含水量和LDMC的改变驱动。这些结果表明，生长季晚期的降水对PUE具有关键影响，同时突显了蒸散量和叶片干物质含量在调控半干旱草原生态系统生产力中的重要性。