Responses and influencing factors of foliar photosynthetic characteristics of <italic>Larix gmelinii </italic>to changing environments

Abstract

Investigating tree photosynthetic capacity is important for understanding the carbon cycles of terrestrial ecosystems and their responses and adaptation to climatic change. Dahurian Larch ( Larix gmelinii ) is one of the dominant tree species in Chinese boreal forests with a broad bio-geographic range under divergent habitats, and thus an ideal tree species for exploring tree adaptation to environment. In this study, we measured the foliar photosynthesis and associated physiological parameters of 30-year-old Dahurian larch trees from six provenances in a common garden at the Maoershan Forest Ecosystem Research Station in Northeast China for three years (2009–2011). The six provenances were located across the natural distribution range of the larch, spanning approximately 4° in latitude (48°–52°N), 5°C in mean annual temperature ( - 2.3–2.6°C), and 200 mm in mean annual precipitation (425–622 mm). To access the top canopy of the sampled trees, we constructed 15-m-high wooden scaffolds at the site. Three representative trees from each provenance were selected for the measurements per month from mid May to mid September. We measured three fully expanded sunlit fascicles on young short shoots at the top of the canopy of each tree in situ with an infrared gas analyzer. On non-rainy days, light and CO2 response curves were measured between 06:30 and 12:00 hours under optimal conditions. Our goal was to explore impacts of environmental changes on foliar photosynthetic characteristics of the larch and their driving factors. The main results were summarized as follows: (ⅰ) The leaf-area-based maximum net photosynthetic rate ( P max-a), dark respiratory rate ( R a), apparent quantum yield (AQY), maximum rate of carboxylation ( V max), maximum electron transport rate ( J max) and triose phosphate utilization rate (TPU) all increased significantly ( P T s) and aridity index (AI) of the seed-source original sites, while the light compensation point (LCP) and photorespiratory rate ( R p) showed an opposite trend. This suggests that the leaf photosynthetic characteristics genetically adapt to the original site conditions of the tree seed-sources, among which the temperature and precipitation are the major driving factors. (ⅱ) P max-a was positively correlated with AQY, V max, J max, TPU, and leaf nitrogen concentration, but negatively with LCP and R p ( P T s habitats had higher sensitivity of P max-a associated with other characteristics. (ⅲ) P max-a was significantly and positively correlated with 3-day mean temperature, mean monthly temperature, mean growing season temperature, 3-day mean relative humidity, and mean monthly precipitation of the common garden, while the R a showed opposite trends with the environmental factors except for the mean growing season temperature. This indicates that the leaf photosynthetic characteristics acclimate to the environmental conditions of the common garden. However, the trees from higher T s habitats had lower intercepts of the regression equations of P max-a associated with the environmental factors, and had the opposite trends for R a except for the mean growing season temperature. The results suggest that the relationships between foliar photosynthetic characteristics and environment are jointly controlled by both phenotypic acclimation to current site conditions and genotypic adaptation to the original environment of the seed-source. These findings provide insights on understanding the survival, reproduction and distribution of Dahurian larch to changing environments.