Qingpeng Yang

Acclimation of Foliar Respiration and Photosynthesis in Response to Experimental Warming in a Temperate Steppe in Northern China

Background Thermal acclimation of foliar respiration and photosynthesis is critical for projection of changes in carbon exchange of terrestrial ecosystems under global warming. Methodology/Principal Findings A field manipulative experiment was conducted to elevate foliar temperature (T leaf) by 2.07°C in a temperate steppe in northern China. R d/T leaf curves (responses of dark respiration to T leaf), A n/T leaf curves (responses of light-saturated net CO2 assimilation rates to T leaf), responses of biochemical limitations and diffusion limitations in gross CO2 assimilation rates (A g) to T leaf, and foliar nitrogen (N) concentration in Stipa krylovii Roshev. were measured in 2010 (a dry year) and 2011 (a wet year). Significant thermal acclimation of R d to 6-year experimental warming was found. However, A n had a limited ability to acclimate to a warmer climate regime. Thermal acclimation of R d was associated with not only the direct effects of warming, but also the changes in foliar N concentration induced by warming. Conclusions/Significance Warming decreased the temperature sensitivity (Q 10) of the response of R d/A g ratio to T leaf. Our findings may have important implications for improving ecosystem models in simulating carbon cycles and advancing understanding on the interactions between climate change and ecosystem functions.

Responses of Pinus massoniana and Pinus taeda to freezing in temperate forests in central China

Abstract Masson pine (Pinus massoniana Lamb.), a native species widely distributed in temperate forests in central China, and Loblolly pine (Pinus taeda L.), an exotic tree species introduced to China from southeastern United States, are dominant evergreen conifers that play a pivotal role in maintaining forest structure and functions for the region. We examined the effects of freezing on these species with chlorophyll fluorescence and electrolyte leakage using both field- and laboratory-based experiments in September 2009 and January 2010, respectively. We found that freezing could cause a greater impact on the Loblolly pine than the Masson pine. Although the two species showed similar values of F v /F m and electrolyte leakage before freezing, the Masson pine needles showed lower F v /F m and higher electrolyte leakage ratios than those of the Loblolly pine when treated in low temperatures (−15 to 0°C). We also found that cold-acclimation was crucial for both species to adapt to low temperatures with the F v /F m ratio decreased approximately by 80% in the first freezing hour for the non-acclimated needles of both species while the cold-acclimated needles showed little changes in the F v /F m ratio. This finding is also supported by our measurements of electrolyte leakage. These results suggest that the Loblolly pine could be more susceptible to freezing damages than the Masson pine in central China.

Thinning effect on photosynthesis depends on needle ages in a Chinese fir (Cunninghamia lanceolata) plantation

Canopies in evergreen coniferous plantations often consist of various-aged needles. However, the effect of needle age on the photosynthetic responses to thinning remains ambiguous. Photosynthetic responses of different-aged needles to thinning were investigated in a Chinese fir (Cunninghamia lanceolata) plantation. A dual isotope approach [simultaneous measurements of stable carbon (δ13C) and oxygen (δ18O) isotopes] was employed to distinguish between biochemical and stomatal limitations to photosynthesis. Our results showed that increases in net photosynthesis rates upon thinning only occurred in the current-year and one-year-old needles, and not in the two- to four-year-old needles. The increased δ13C and declined δ18O in current year needles of trees from thinned stands indicated that both the photosynthetic capacity and stomatal conductance resulted in increasing photosynthesis. In one-year-old needles of trees from thinned stands, an increased needle δ13C and a constant needle δ18O were observed, indicating the photosynthetic capacity rather than stomatal conductance contributed to the increasing photosynthesis. The higher water-soluble nitrogen content in current-year and one-year-old needles in thinned trees also supported that the photosynthetic capacity plays an important role in the enhancement of photosynthesis. In contrast, the δ13C, δ18O and water-soluble nitrogen in the two- to four-year-old needles were not significantly different between the control and thinned trees. Thus, the thinning effect on photosynthesis depends on needle age in a Chinese fir plantation. Our results highlight that the different responses of different-aged needles to thinning have to be taken into account for understanding and modelling ecosystem responses to management, especially under the expected environmental changes in future.

Different responses of non-structural carbohydrates in above-ground tissues/organs and root to extreme drought and re-watering in Chinese fir (Cunninghamia lanceolata) saplings

Key messageThe total NSC concentration in the roots declined more significantly than in the above-ground tissues/organs under drought treatment, and the level did not return to that of the control after re-watering.AbstractNon-structural carbohydrates (NSC) reflect the relative balance between C-gain (photosynthesis) and C-loss (respiration) and play a pivotal role in carbon cycling in a forest ecosystem. However, little is known regarding the effects of extreme drought and re-watering on the NSC status in different tissues/organs. This study examined the variation in NSC concentrations in different tissues/organs and the total NSC pool sizes in Chinese fir (Cunninghamia lanceolata) saplings after drought and re-watering. Results showed that significant differences were observed in the concentrations of total NSC and its components in the different tissues/organs. For example, the NSC concentrations were nine times higher in bark than in stemwood. Moreover, the responses of NSC and its components to extreme drought also varied in different tissues/organs. Drought either significantly increased or maintained the total NSC concentration in the above-ground tissues/organs. By contrast, drought reduced the total NSC concentration in the sapling roots. Furthermore, the results also showed that extreme drought leads to sapling death, which is supported by the result of needle staining and the failure of the total NSC concentration to recover after re-watering. The concentrations of NSC and its components further decreased, and a more pronounced decline was observed in the roots than in the above-ground tissues/organs after re-watering. We speculated that drought can cause failure in carbon translocation between the above- and below-ground tissues/organs and thus cause varied responses of different tissues/organs to extreme drought and re-watering. Overall, these findings suggest the need to investigate the potential differential responses of various tissues/organs to climate change.

Response of nonstructural carbohydrates to thinning and understory removal in a Chinese fir [ Cunninghamia lanceolata (Lamb.) Hook] plantation

Key messageThis work provides insight into the functional changes in above- and belowground tree tissues/organs after thinning and understory removal.AbstractNon-structural carbon (NSC), which reflects the relationship between the carbon source and carbon sink, plays a key role in the carbon cycle in forest ecosystems. Although thinning and understory removal are two common measures in plantation management, limited information is available on the effects of thinning and understory removal on the NSC of plants, particularly of different tissues/organs. This study investigated the response of the NSC (soluble sugars and starch) concentration of different tissues/organs (current- to 4-year-old needles, inner-bark, xylem, and coarse and fine roots) toward thinning and understory removal in a plantation of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook), which is an evergreen coniferous species. Results showed that thinning significantly increased the NSC concentration of the needles. The NSC concentrations of the inner-bark and xylem did not respond to thinning. In contrast to the aboveground tissues/organs, the NSC concentration of the coarse root was significantly reduced by thinning. Thus, the thinning-induced NSC response of the above- and belowground tissues/organs varied, indicating that the NSC was remobilized after thinning. However, understory removal had a very reduced effect on the NSC concentration of all the mentioned above- and belowground tissues/organs. Our findings suggest the need to simultaneously consider above- and belowground tissues/organs in future forest management studies.

Rainfall-dependent influence of snowfall on species loss

The response of plant diversity to increased snowfall, i.e., precipitation that falls in a solid state rather than a liquid state, is unclear. We investigated the potential effects of 12 year snowfall augmentation on species richness using coordinated distributed experiments, including ten sites across a rainfall gradient of 211–354 mm and spanning 440 km in length in the temperate steppe. Snowfall augmentation decreased species richness rather than enhancing it. Abiotic factor driven by soil pH was the dominant determinant affecting the variation in species richness under changing precipitation regimes, overriding biotic factor. The strongest reduction in species richness induced by snowfall augmentation occurred in the low-rainfall sites. Our study provides insights into the relationship between precipitation and biodiversity in arid and semiarid regions.