The response of microbial communities to continual and prolonged water exposure provides useful insight when facing global climate changes that cause increased and uneven precipitation and extreme rainfall events. In this study, we investigated an in situ manipulative experiment with four levels of water exposure (ambient precipitation +0%, +25%, +50%, and +100% of local annual mean precipitation) in a desert ecosystem of China. After 9 years of water addition, Illumina sequencing was used to analyze taxonomic compositions of the soil bacterial, archaeal, and fungal communities. The results showed significant increases in microbial biomass carbon (MBC) at higher amended precipitation levels, with the highest values reported at 100% precipitation. Furthermore, an increase in the bacterial species richness was observed along the water addition gradient. In addition, the relative abundance of several bacterial phyla, such as Proteobacteria, significantly increased, whereas that of some drought-tolerant taxa, including Actinobacteria, Firmicutes, and Bacteroidetes, decreased. In addition, the phyla Planctomycetes and Nitrospirae, associated with nitrification, positively responded to increased precipitation. Archaeal diversity significantly reduced under 100% treatment, with changes in the relative abundance of Thaumarchaeota and Euryarchaeota being the main contributors to shifts in the archaeal community. The fungal community composition was stable in response to water addition. Results from the Mantel test and structural equation models suggested that bacterial and archaeal communities reacted contrastingly to water addition. Bacterial community composition was directly affected by changing soil moisture and temperature, while archaeal community composition was indirectly affected by changing nitrogen availability. These findings highlight the importance of soil moisture and nitrogen in driving microbial responses to long-term precipitation changes in the desert ecosystem.

Climate models often predict that more extreme precipitation events will occur in arid and semiarid regions, where plant phenology is particularly sensitive to precipitation changes. To understand how increases in precipitation affect plant phenology, this study conducted a manipulative field experiment in a desert ecosystem of northwest China. In this study, a long-term in situ water addition experiment was conducted in a temperate desert in northwestern China. The following five treatments were used: natural rain plus an additional 0, 25, 50, 75, and 100% of the local mean annual precipitation. A series of phenological events, including leaf unfolding (onset, 30%, 50%, and end of leaf unfolding), cessation of new branch elongation (30, 50, and 90%), and leaf coloration (80% of leaves turned yellow), of the locally dominant shrub Nitraria tangutorum were observed from 2012 to 2018. The results showed that on average, over the seven-year-study and in all treatments water addition treatments advanced the spring phenology (30% of leaf unfolding) by 1.29–3.00 days, but delayed the autumn phenology (80% of leaves turned yellow) by 1.18–11.82 days. Therefore, the length of the growing season was prolonged by 2.11–13.68 days, and autumn phenology contributed more than spring phenology. In addition, water addition treatments delayed the cessation of new branch elongation (90%) by 5.82–12.61 days, and nonlinear relationships were found between the leaves yellowing (80% of leaves) and the amount of watering. Linear relationships were found between the cessation of new branch elongation (90%), the length of the growing season, and amount of water addition. The two response patterns to water increase indicated that predictions of phenological events in the future should not be based on one trend only.

Plant phenology is the most sensitive biological indicator that responds to climate change. Many climate models predict that extreme precipitation events will occur frequently in the arid areas of northwest China in the future, with an increase in the quantity and unpredictability of rain. Future changes in precipitation will inevitably have a profound impact on plant phenology in arid areas. A recent study has shown that after the simulated enhancement of precipitation, the end time of the leaf unfolding period of Nitraria tangutorum advanced, and the end time of leaf senescence was delayed. Under extreme climatic conditions, such as extremely dry or wet years, it is unclear whether the influence of the simulated enhancement of precipitation on the phenology of N. tangutorum remains stable. To solve this problem, this study systematically analyzed the effects of the simulated enhancement of precipitation on the start, end and duration of four phenological events of N. tangutorum, including leaf budding, leaf unfolding, leaf senescence and leaf fall under extremely dry and wet conditions. The aim of this study was to clarify the similarities and differences of the effects of the simulated enhancement of precipitation on the start, end and duration of each phenological period of N. tangutorum in an extremely dry and an extremely wet year to reveal the regulatory effect of extremely dry and excessive amounts of precipitation on the phenology of N. tangutorum. (1) After the simulated enhancement of precipitation, the start and end times of the spring phenology (leaf budding and leaf unfolding) of N. tangutorum advanced during an extremely dry and an extremely wet year, but the duration of phenology was shortened during an extremely wet year and prolonged during an extremely drought-stricken year. The amplitude of variation increased with the increase in simulated precipitation. (2) After the simulated enhancement of precipitation, the start and end times of the phenology (leaf senescence and leaf fall) of N. tangutorum during the autumn advanced in an extremely wet year but was delayed during an extremely dry year, and the duration of phenology was prolonged in both extremely dry and wet years. The amplitude of variation increased with the increase in simulated precipitation. (3) The regulation mechanism of extremely dry or wet years on the spring phenology of N. tangutorum lay in the different degree of influence on the start and end times of leaf budding and leaf unfolding. However, the regulation mechanism of extremely dry or wet years on the autumn phenology of N. tangutorum lay in different reasons. Water stress caused by excessive water forced N. tangutorum to start its leaf senescence early during an extremely wet year. In contrast, the alleviation of drought stress after watering during the senescence of N. tangutorum caused a delay in the autumn phenology during an extremely dry year.

Desert ecosystem CO₂ exchange may play an important role in global carbon cycling. However, it is still not clear how the CO₂ fluxes of shrub-dominated desert ecosystems respond to precipitation changes. We performed a 10-year long-term rain addition experiment in a Nitraria tangutorum desert ecosystem in northwestern China. In the growing seasons of 2016 and 2017, with three rain addition treatments (natural precipitation +0%, +50%, and +100% of annual average precipitation), gross ecosystem photosynthesis (GEP), ecosystem respiration (ER), and net ecosystem CO₂ exchange (NEE) were measured. The GEP responded nonlinearly and the ER linearly to rain addition. The NEE presented a nonlinear response along the rain addition gradient, with a saturation threshold by rain addition between +50% and +100%. The growing season mean NEE ranged from −2.25 to −5.38 μmol CO₂ m⁻² s⁻¹, showing net CO₂ uptake effect, with significant enhancement (more negative) under the rain addition treatments. Although natural rainfall fluctuated greatly in the growing seasons of 2016 and 2017, reaching 134.8% and 44.0% of the historical average, the NEE values remained stable. Our findings highlight that growing season CO₂ sequestration in desert ecosystems will increase against the background of increasing precipitation levels. The different responses of GEP and ER of desert ecosystems under changing precipitation regimes should be considered in global change models.

Fruit setting and ripening are crucial in the reproductive cycle of many desert plant species, but their response to precipitation changes is still unclear. To clarify the response patterns, a long-term in situ water addition experiment with five treatments, namely natural precipitation (control) plus an extra 25%, 50%, 75%, and 100% of the local mean annual precipitation (145 mm), was conducted in a temperate desert in northwestern China. A whole series of fruiting events including the onset, peak, and end of fruit setting and the onset, peak, and end of fruit ripening of a locally dominant shrub, Nitraria tangutorum, were observed from 2012 to 2018. The results show that (1) water addition treatments had no significant effects on all six fruiting events in almost all years, and the occurrence time of almost all fruiting events remained relatively stable compared with leaf phenology and flowering phenology after the water addition treatments; (2) the occurrence times of all fruiting events were not correlated to the amounts of water added in the treatments; (3) there are significant inter-annual variations in each fruiting event. However, neither temperature nor precipitation play key roles, but the preceding flowering events drive their inter-annual variation.

Seed release is crucial in the reproductive cycle of many desert plant species, but their responses to precipitation changes are still unclear. To clarify the response patterns, we conducted a long-term in situ water addition experiment with five treatments, including natural precipitation (control) plus an extra 25%, 50%, 75%, and 100% of the local mean annual precipitation (145 mm), in a temperate desert in northwestern China. Both the onset and end of the seed release phenophase of the locally dominant shrub, Nitraria tangutorum, were observed from 2012 to 2018. The results showed that both the onset and end time of seed release, especially the end time, were significantly affected by water addition treatment. On average, the end time of seed release was advanced by 3.9 d, 7.3 d, 10.8 d, and 3.8 d under +25%, +50%, +75%, and +100% water addition treatments, respectively, over the seven-year study, compared with the control. The changes in the onset time were relatively small (only several hours), and the duration of seed release was shortened by 4.0 d, 7.5 d, 10.8 d, and 2.0 d under +25%, +50%, +75%, and +100% water addition treatments, respectively. The onset and end time of seed release varied greatly between the years. Preceding fruit ripening and summer temperature jointly regulated the inter-annual variation of the onset time of seed release, while the cumulative summer precipitation played a key role in driving the inter-annual variation of the end time. The annual mean temperature controlled the inter-annual variation of the seed release duration, and these interactions were all non-linear.