Relationships of soil phosphorus status to wood anatomical traits and to nutrient translocation in woody plants
Final Report Abstract
The research project investigated how soil phosphorus status affects wood anatomy and nutrient recycling from ageing tissue in evergreen Australian tree species growing along a soil fertility gradient. In particular it focused on relationships between nutrients and wood parenchymatic tissue which consists of living cells. Due to the low phosphorus (P) availability in many soils worldwide, plants have to use different adaptative strategies to either optimize their nutrient uptake and/or reduce their nutrient losses to maintain photosynthesis and growth. In the project agenda, both practical work in the forests as well as the greenhouse experiment were successful, despite the tight time schedule. Additionally, a software to distinguish cell types based on cell size and color was developed in cooperation with a software programmer. The Java-based 'Cell-IT' software might be used for related wood anatomical investigations in further research projects. The implementation of the fieldwork and following analyses was conducted without major methodological or technical difficulties. Only the local rocky soil conditions did not allow for a sensible realization of the planed root investigations. The results from the present study confirm that parenchyma abundance in wood does vary widely across and much less plastically within species with similar patterns in twig and stem wood. Contrary to expectations, there was no clear relationships neither between parenchyma abundance and nutrient concentrations in woody tissue nor between parenchyma and soil nutrients. As the remaining wood tissue - namely fiber cells and conduits - have relatively constant nutrient concentrations, it can be inferred that there must be pronounced differences in nutrient concentration amongst the parenchyma cells themselves. Variable metabolic activity or parenchyma cells that are used as adjustable nutrient storage could explain the differences between and within species in parenchyma nutrient concentrations. It was further confirmed here that species on low nutrient soils show on average higher nutrient recycling efficiencies particularly from aging leaves. Also, P was recycled more efficiently than N from both leaves and stem wood. Nevertheless, the wood recycling efficiencies observed showed a wide scatter. Surprisingly, we found negative recycling efficiencies in the wood of a few species, in other words concentrations in the inner heartwood were higher than in the outer sapwood. Using data collected in this project and assumptions based on the pipe model theory, the contribution of wood to whole-tree nutrient budget was estimated. According to the calculations the wood demand is strongly depending on tree height surpassing leaf demand at around 8m height (for N) and 11m (for P). Consequently, the construction costs of wood in terms of nutrient units may even limit tree height growth under certain circumstances. This characterizes as major influencing factor which has been largely underrepresented by the scientific literature. Even after finalizing this project, the adaptive functions of the variability in parenchymatic wood tissue remain unresolved. Measuring the type and distribution of structural and non-structural nutrients might shed light on the question why parenchyma-rich tissue is not in general nutrient-rich tissue. Using integrated molecular and biophysical techniques can help us in future projects to investigate differences in the nutrient concentration in isolated parenchyma and to understand wood anatomical functionality related to whole‐plant nutrient budgets.
