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• Elevated [CO 2 ] and temperature jointly stimulated leaf A net before heading. • Air warming accelerated photosynthetic down-regulation under CO 2 enrichment after heading. • G s acclimated to warming and CO 2 enrichment in parallel with A net under no stress conditions. • Earlier leaf senescence, larger sink capacity or lower rice sterility might cause photosynthetic acclimation. • Co-elevation of [CO 2 ] and temperature increased dry matter productivity in Chinese double rice cultivation. Changes in atmospheric CO 2 concentration ([CO 2 ]) and temperature have impacts on leaf photosynthesis (A net) and stomatal conductance (G s) of rice, which strongly affect dry matter productivity. Understanding of the acclimation responses of A net and G s under elevated [CO 2 ] and/or temperature is limited. A field experiment of double rice (early rice-late rice rotation) was conducted using open-top chambers from 2013 to 2016 in Hubei Province, Central China, with two levels of [CO 2 ] (ambient, ambient + 60 μmol mol−1) and two levels of temperature (ambient, ambient + 2°C). Averaging across the four-year experiment, elevated [CO 2 ] and elevated temperature increased A net by 2.4 %–9.4 % and 2.4 %–10.7 %, respectively at pre-heading stages. A positive interaction was observed between elevated [CO 2 ] and temperature in early rice which further increased A net , while the interaction was not additive in late rice. Elevated [CO 2 ] caused lower G s and partly offset the stimulation of elevated temperature on G s at tillering and jointing. At post-heading stages, photosynthetic acclimation to elevated [CO 2 ] was observed as the stimulation of A net was not continued. Elevated temperature decreased A net by 1.7 %–16.6 % and further accelerated photosynthetic down-regulation by elevated [CO 2 ]. Warming reduced G s at milking and maturity in early rice because of high ambient temperature, which resulted in stomatal limitation to photosynthesis, but its effects on G s in late rice were positive because the ambient temperature was low. Generally, G s acclimated to warming and CO 2 enrichment in parallel with A net when there were no environmental constraints. Earlier leaf senescence, decreased leaf SPAD, lower seed-setting rate or larger sink capacity caused by elevated [CO 2 ] and/or temperature might directly or indirectly explain the down-regulation on photosynthesis after heading. Our results show that warming alters the acclimation of leaf photosynthesis and stomatal conductance to CO 2 enrichment and the combined effects differ between growth stages, and indicate that co-elevation of [CO 2 ] and temperature may increase dry matter productivity in the Chinese double rice cropping system. [ABSTRACT FROM AUTHOR]

Climate change and anthropogenic activities have resulted in increased atmospheric methane (CH 4) concentration. Increased nitrogen deposition and precipitation accompanies climate warming and can change soil carbon and nitrogen dynamics and microbial processes and alter CH 4 fluxes. To quantify the sink of the vast alpine meadows of the Tibetan Plateau and to examine how precipitation addition (P), warming (W), and nitrogen addition (N) affect CH 4 fluxes in alpine meadows, we conducted continuous 3-growing season experiments in an alpine meadow using the static chamber and gas chromatograph method. Soil CH 4 samples were collected during the early, peak, and late stages of the growing season from 2015 to 2017. Our results suggested that neither P, W, nor N had an interaction effect on soil CH 4 uptake. P significantly increased and decreased the copies number of particulate methane monooxygenase alpha subunit (pmoA) and methyl-coenzyme M reductase alpha subunit (mcrA), respectively. However, P significantly decreased CH 4 uptake, particularly under the combined treatment of P and N. Compared with the control, CH 4 uptake decreased under P, N, PW, and PN by 50.64%, 6.24%, 39.37%, and 75.06%, respectively, whereas under W and WN CH 4 uptake increased by 16.19% and 7.56%, respectively. Soil CH 4 uptake was positively correlated with soil temperature and pmoA and negatively correlated with soil moisture and NH 4 +-N content. CH 4 uptake was significantly affected by the sampling period. CH 4 uptake was significantly lower rates during peak growing season compared with those during the early and late stages of the growing season. Our results suggest that, (1) CH 4 fluxes of alpine grassland ecosystems are more sensitive to P than W or N, and (2) precipitation controls CH 4 flux response to increasing nitrogen deposition in alpine meadows on the Tibetan Plateau. Therefore, future research should focus on the response and feedback of CH 4 uptake to changes in precipitation. Unlabelled Image • Neither nitrogen addition nor warming significantly affected CH 4 uptake in the alpine meadows. • Increased precipitation significantly decreased CH 4 uptake, particularly under the combined treatment of P and N. • CH 4 uptake in the alpine meadows was most significantly affected by changes in precipitation. [ABSTRACT FROM AUTHOR]

Ecosystem stability is one of the main factors maintaining ecosystem functioning and is closely related to temporal variability in productivity. Resistance and resilience reflect tolerance and recovering ability, respectively, of a plant community under perturbation, which are important for maintaining the stability of ecosystems. Generally, heavy grazing reduces the stability of grassland ecosystems, causing grassland degradation. However, how livestock grazing affects ecosystem stability is unclear in alpine steppe ecosystems. We conducted a five-year grazing experiment with Tibetan sheep in a semi-arid alpine steppe on the Qinghai-Tibetan Plateau, China. The experimental treatments included no grazing (NG), light grazing (LG, 2.4 sheep per ha), moderate grazing (MG, 3.6 sheep per ha) and heavy grazing (HG, 6.0 sheep ha). We calculated resistance and resilience of three plant functional groups and ecosystem stability under the three grazing intensities using aboveground primary productivity. The results showed that with increasing grazing intensity, aboveground biomass of each functional group significantly decreased. As grazing intensity increased, the resistance of forbs first increased then decreased. The resilience of graminoids in HG was significantly lower than in LG plots, but the resilience of legumes in HG was higher than in LG and MG plots. The resilience of graminoids was significantly higher than legume and forbs under LG and MG treatments. In HG treatments, resilience of legumes was higher than graminoids and forbs. Ecosystem stability did not change under different grazing intensities, because of dissimilar performance of the resilience and resistance of functional groups. Our results highlight how the differential resistance and resilience of different function groups facilitate the tolerance of alpine steppe to grazing under even a heavy intensity. However, the degradation risk of alpine steppe under heavy grazing still needs to be considered in grassland management due to sharp decreases of productivity. • Grazing intensity have no significant effects on plant resistance. • Resilience of graminoids under heavy grazing was lower than other treatments. • Under heavy grazing, resilience of legumes was higher than graminoids and forbs. • Ecosystem stability did not change under different grazing intensities. [ABSTRACT FROM AUTHOR]

• Responses to warming differed between early rice and late rice. • Warming benefited yield formation before heading. • Benefits of CO 2 enrichment could eliminate the negative effects of warming on yield. • Yield may not decrease under future climate change in Chinese double rice system. Elevated atmospheric CO 2 concentration ([CO 2 ]) and temperature can strongly affect rice (Oryza sativa L.) production. However, the impact of warming is variable depending on ambient temperature and cropping system. Little is known about the effect of elevated temperature and its interaction with elevated [CO 2 ] in the Chinese double rice cropping system. To study this issue, field experiments were conducted using open-top chambers (OTC) with varying [CO 2 ] (ambient, ambient+60 μmol mol−1) and varying temperature (ambient, ambient+2 °C) for 4 rotations of double rice from 2013 to 2016. Elevated [CO 2 ] significantly increased grain yield in both early rice and late rice. This could be attributed to greater aboveground biomass, higher panicle number (m-2), spikelet number (per panicle) and 1000-grain weight. Elevated temperature decreased yield in early rice (except for 2016) due to decreases in % filled grains and 1000-grain weight. Elevated temperature increased yield in late rice due to increases in aboveground biomass, number of panicles and spikelets, although % filled grains decreased. We found that warming had positive effects on tiller development and dry matter accumulation during the pre-heading period both in early and late rice, which contributed to yield formation. When elevated temperature and [CO 2 ] were combined, yield changed by −1.9–23.7% in early rice compared with ambient condition as warming partly offset the benefits of CO 2 enrichment, while yield increased by 14.3–18.8% in late rice due to a synergy between warming and CO 2 enrichment. The benefits of CO 2 enrichment for fertile spikelets (m-2) and aboveground biomass could reduce or eliminate the negative impacts of warming. However, there were no significant interactions between elevated temperature and [CO 2 ] in most rice seasons. Our findings indicate that warming by 2 °C is not detrimental to yield formation under CO 2 enrichment, and suggest that grain yield may not decrease under future climate change in the Chinese double rice cropping system. [ABSTRACT FROM AUTHOR]