Yunpu Zheng

Effects of experimental warming on stomatal traits in leaves of maize (Zea may L.)

We examined the warming effects on the stomatal frequency, stomatal aperture size and shape, and their spatial distribution pattern of maize (Zea may L.) leaves using a light microscope, an electron scanning microscope, and geostatistic techniques. A field manipulative experiment was conducted to elevate canopy temperature by 2.08°C, on average. We found that experimental warming had little effect on stomatal density, but significantly increased stomatal index due to the reduction in the number of epidermal cells under the warming treatment. Warming also significantly decreased stomatal aperture length and increased stomatal aperture width. As a result, warming significantly increased the average stomatal aperture area and stomatal aperture circumference. In addition, warming dramatically changed the stomatal spatial distribution pattern with a substantial increase in the average nearest neighbor distance between stomata on both adaxial and abaxial surfaces. The spatial distribution pattern of stomata was scale dependent with regular patterns at small scales and random patterns at larger scales on both leaf surfaces. Warming caused the stomatal distribution to become more regular on both leaf surfaces with smaller L(t) values (Ripleys K-function, L(t) is an expectation of zero for any value of t) in the warming plots than the control plots.

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.

Climatic information improves statistical individual-tree mortality models for three key species of Sichuan Province, China

Abstract• Key messageClimate variables improve individual-tree mortality models for fir, oak and birch.• ContextClimate is considered as an important driver of tree mortality, but few studies have included climate factors in models to explore their importance for modelling individual-tree mortality.• AimsTo measure the performance of climate-based models, we built individual-tree mortality models using individual, stand, and climate variables for fir (Abies faxoniana Rehd. et Wils.), oak (Quercus aquifolioides Rehd. et Wils.), and birch (Betula albo-sinensis Burk.) in Southwest China, and explored the corresponding effects on tree death.• MethodsWe developed tree mortality models based on 287 permanent plots from the Sichuan Forest Inventory data, and compared the models based on variables of individual (I), stand (S), and climate (C) levels, and different combinations (I + S, I + C, S + C, I + S + C) among these groups to improve model performance. We employed relative Akaike information criterion (AIC), area under receiver operating characteristic curve (AUC), and Hosmer-Lemeshow’s goodness-of-fit statistic for model evaluation and validation.• ResultsWe found that tree mortalities of the three species could be better predicted (AUC > 0.8) by carefully selecting variables at three ecological scales (individual, stand, and regional climate). Our results suggest that the higher mortality of the object trees occurs when they endure lower radial growth of the previous years, more intensive competition, and moderate canopy cover (for birch), while lower mortality was seen in an appropriate range of climate conditions and at higher stand canopy cover (for fir and oak).• ConclusionThe results have significance for incorporating the effects of a changing climate into mortality models.