Resource availability, productivity, and diversity in plants have often been described as interrelated, and exhibit a monotonic decline with increasing elevation. Mounting evidence, however, suggests a peak in diversity at mid-elevation levels where intermediate resource availability may maximize productivity. Although several studies have provided insights into the independent mechanisms of how plants respond to resource limitations, understanding the processes of how multiple resources interact are still unresolved, particularly with respect to forest regeneration success across the elevations. We hypothesized that there are complex interactions between resources, and seedlings will perform better when growing environments best matched to their seed source environments. Seeds collected from three elevations (310, 1220 and 1970 masl; of Hilo to Mauna Kea) were grown in a common garden. Light (full sunlight vs 25% of full sunlight) and nitrogen (standard dose vs no) treatments were randomized across seed sources in wet (80% FC) and dry (25% FC) conditions for three months. Leaf water potentials (LWP), Photosynthesis and transpiration rate (An, Tr), N and C concentrations, total plant dry matter, shoot/root ratios, followed by shoot non-structural carbohydrate (sugar, starch) were quantified.
Results/Conclusions
LWP was more negative for seed source from high of wet conditions, while the opposite trends were observed in dry conditions. An increased with increasing seed source elevations both in wet and dry conditions. Nitrogen addition decreased LWP at low, and increased at high elevation seed sources in any conditions. High starch, and sugar were observed at mid, limitation of N and water decreased starch in low, and light reduced at high elevation seed sources. Seedling root collar diameter and shoot: root ratios specified that seed source from mid elevation perform better in any environmental stress, which was supported by measured physiological and biochemical traits. Water and then nitrogen are the main limiting factors in low, and light is the main limiting factor in the high elevation. Seed backgrounds from high were more tolerate to stress in comparison to low, while mid elevations buffered some of these stresses. Based on our findings, restoration strategies that consider the adaptability and stress tolerance associated with elevation range may be beneficial as seedling response was tightly linked to seed source environments.