Over the past decades, drought events have been widely reported in almost all forest biomes around the world. Substantial evidence has suggested that trees might exhibit remarkable phenotypic plasticity in their eco-physiological traits in response to water deficit. However, current studies on trait plasticity are mainly concentrated on growth components, research on how reproductive traits respond to extreme drought is still lacking. It therefore limits our ability to synthetically predict how the ecophysiological properties of trees adapt to climate change.

Dr. He Peng, a PhD student from Institute of Applied Ecology (IAE), Chinese Academy of Sciences. He and his colleagues in IAE and other professors from Swiss Federal Institute for Forest, Snow and Landscape Research WSL, conducted a study to explore how pine trees adjust their reproductive strategies in terms of single reproductive traits, multidimensional trait diversity and trade-offs between growth and reproductive in a comprehensive way.

By combining a natural precipitation transect study in China (Pinus. sylvestris var. mongolica forests) with a long-term precipitation manipulation experiment in Switzerland (Pinus. Sylvestris forests), their study can thus cover a broad gradient of water availability and different spatio-temporal scales, and thus to detect different plant response mechanisms.

Two main results were found in their work. Firstly, their results showed that both cone richness (TOP) and divergence (FDis) declined with increasing aridity, suggesting that the inviable cone phenotypes would be filtered out by severe drought stress, and only optimal phenotypes that maximized reproductive performance could survive. This result supports the ‘environmental filtering hypothesis’.

On the contrary, they observed that seed evenness (TED) increased with increasing drought severity in the irrigation experiment, demonstrating that pine trees may maximize seed trait dissimilarity in multiple dimensions as a strategy to minimize competition among individuals under harsh conditions. This result confirms the ‘niche partitioning hypothesis’. Secondly, they found the trade-offs between reproduction and vegetative growth were only observed in the transect study, highlighting that the reproduction of these trees occurs at the expense of growth (‘resource switching hypothesis’).

By contrast, the trade-offs between growth and reproduction were not observed in the irrigation experiment, suggesting that the pine trees in this experiment have the ability to match the absorbed resources to maximize their all performances (both growth and reproduction) (‘resource matching hypothesis’).

The study entitled “Scale dependent responses of pine reproductive traits to experimental and natural precipitation gradients” has been published in Environmental and Experimental Botany.

The study is financially supported by the National Natural Science Foundation of China.