ATP as Phosphorus and Nitrogen Source for Nutrient Uptake by Fagus sylvatica and Populus x canescens Roots.

The present study elucidated whether roots of temperate forest trees can take up organic phosphorus in the form of ATP. Detached non-mycorrhizal roots of beech (Fagus sylvatica) and gray poplar (Populus x canescens) were exposed under controlled conditions to 33P-ATP and/or 13C/15N labeled ATP in the presence and absence of the acid phosphatase inhibitor MoO4 2-. Accumulation of the respective label in the roots was used to calculate 33P, 13C and 15N uptake rates in ATP equivalents for comparison reason. The present data shown that a significant part of ATP was cleaved outside the roots before phosphate (Pi) was taken up. Furthermore, nucleotide uptake seems more reasonable after cleavage of at least one Pi unit as ADP, AMP and/or as the nucleoside adenosine. Similar results were obtained when still attached mycorrhizal roots of adult beech trees and their natural regeneration of two forest stands were exposed to ATP in the presence or absence of MoO4 2-. Cleavage of Pi from ATP by enzymes commonly present in the rhizosphere, such as extracellular acid phosphatases, ecto-apyrase and/or nucleotidases, prior ADP/AMP/adenosine uptake is highly probable but depended on the soil type and the pH of the soil solution. Although uptake of ATP/ADP/AMP cannot be excluded, uptake of the nucleoside adenosine without breakdown into its constituents ribose and adenine is highly evident. Based on the 33P, 13C, and 15N uptake rates calculated as equivalents of ATP the 'pro and contra' for the uptake of nucleotides and nucleosides is discussed. Short Summary Roots take up phosphorus from ATP as Pi after cleavage but might also take up ADP and/or AMP by yet unknown nucleotide transporter(s) because at least the nucleoside adenosine as N source is taken up without cleavage into its constituents ribose and adenine.

N2-fixing black locust intercropping improves ecosystem nutrition at the vulnerable semi-arid Loess Plateau region, China.

The Loess Plateau in northwestern China constitutes one of the most vulnerable semi-arid regions in the world due to long-term decline in forest cover, soil nutrient depletion by agricultural use, and attendant soil erosion. Here, we characterize the significance of N2-fixing Robinia pseudoacacia L. and non-N2-fixing Juglans regia L. for improving nutrient availability and water retention in soil by comparing a range of biological and physicochemical features in monoculture and mixed plantations of both species. We found that N2-fixing Robinia facilitates the nitrogen and phosphorus composition of non-N2-fixing Juglans in the mixed stand as a consequence of improved soil nutrient availability, evident as higher levels of nitrogen and labile carbon compared to mono-specific stands. This demonstrates that intercropping N2-fixing Robinia with non-N2-fixing woody plants can greatly improve soil carbon and nitrogen bioavailability as well as whole-plant nutrition and can potentially mediate water retention with additional sequestration of soil organic carbon in the range of 1 t C ha-1 year-1. Thus, intercropping N2-fixing woody species (e.g. Robinia pseudoacacia or Hippophae rhamnoides L.) with locally important non-N2-fixing tree and shrub species should be considered in afforestation strategies for landscape restoration.

Phosphorus nutrition of Populus × canescens reflects adaptation to high P-availability in the soil.

Phosphorus (P) constitutes one of five macronutrients essential for plant growth and development due to the central function of phosphate in energy metabolism, inheritance and metabolic control. In many ecosystems, plant available soil-P gets limited by soil aging. Hence, plants have developed adaptation strategies to cope with such limitation by an efficient plant and ecosystem internal P-cycling during annual growth. The natural floodplain habitat of fast-growing Populus × canescens is characterized by high soil-P availability. It was thus expected that the P-nutrition of P. × canescens had adapted to this conditions. Therefore, different P-fractions in different twig tissues were investigated during two annual growth cycles. The P-nutrition of P. × canescens markedly differs from that of European beech grown at low soil-P availability (Netzer F, Schmid C, Herschbach C, Rennenberg H (2017) Phosphorus-nutrition of European beech (Fagus sylvatica L.) during annual growth depends on tree age and P-availability in the soil. Environ Exp Bot 137:194-207). This was mainly due to a lack of tree internal P-cycling during annual growth indicated by the absence of P-storage and remobilization in twig bark and wood. Hence, strategies to economize P-nutrition and to prevent P-losses had not developed. This fits with the fast-growth strategy of P. × canescens at unrestricted P-availability. Hence, the P-nutrition strategy of P. × canescens can be seen as an evolutionary adaptation to its natural growth habitat.

Seasonal Alterations in Organic Phosphorus Metabolism Drive the Phosphorus Economy of Annual Growth in F. sylvatica Trees on P-Impoverished Soil.

Phosphorus (P) is one of the most important macronutrients limiting plant growth and development, particularly in forest ecosystems such as temperate beech (Fagus sylvatica) forests in Central Europe. Efficient tree internal P cycling during annual growth is an important strategy of beech trees to adapt to low soil-P. Organic P (Porg) is thought to play a decisive role in P cycling, but the significance of individual compounds and processes has not been elucidated. To identify processes and metabolites involved in P cycling of beech trees, polar-metabolome and lipidome profiling was performed during annual growth with twig tissues from a sufficient (Conventwald, Con) and a low-soil-P (Tuttlingen, Tut) forest. Autumnal phospholipid degradation in leaves and P export from senescent leaves, accumulation of phospholipids and glucosamine-6-phosphate (GlcN6P) in the bark, storage of N-acetyl-D-glucosamine-6-phosphate (GlcNAc6P) in the wood, and establishing of a phospholipid "start-up capital" in buds constitute main processes involved in P cycling that were enhanced in beech trees on low-P soil of the Tut forest. In spring, mobilization of P from storage pools in the bark contributed to an effective P cycling. Due to the higher phospholipid "start-up capital" in buds of Tut beeches, the P metabolite profile in developing leaves in spring was similar in beech trees of both forests. During summer, leaves of Tut beeches meet their phosphate (Pi) needs by replacing phospholipids by galacto- and sulfolipids. Thus, several processes contribute to adequate Pi supply on P impoverished soil thereby mediating similar growth of beech at low and sufficient soil-P availability.

Metabolome and Lipidome Profiles of Populus × canescens Twig Tissues During Annual Growth Show Phospholipid-Linked Storage and Mobilization of C, N, and S.

The temperate climax tree species Fagus sylvatica and the floodplain tree species Populus × canescens possess contrasting phosphorus (P) nutrition strategies. While F. sylvatica has been documented to display P storage and mobilization (Netzer et al., 2017), this was not observed for Populus × canescens (Netzer et al., 2018b). Nevertheless, changes in the abundance of organic bound P in gray poplar trees indicated adaptation of the P nutrition to different needs during annual growth. The present study aimed at characterizing seasonal changes in metabolite and lipid abundances in gray poplar and uncovering differences in metabolite requirement due to specific needs depending on the season. Seasonal variations in the abundance of (i) sugar-Ps and phospholipids, (ii) amino acids, (iii) sulfur compounds, and (iv) carbon metabolites were expected. It was hypothesized that seasonal changes in metabolite levels relate to N, S, and C storage and mobilization. Changes in organic metabolites binding Pi (Porg) are supposed to support these processes. Variation in triacylglycerols, in sugar-phosphates, in metabolites of the TCA cycle and in the amino acid abundance of poplar twig buds, leaves, bark, and wood were found to be linked to changes in metabolite abundances as well as to C, N, and S storage and mobilization processes. The observed changes support the view of a lack of any P storage in poplar. Yet, during dormancy, contents of phospholipids in twig bark and wood were highest probably due to frost-hardening and to its function in extra-plastidic membranes such as amyloplasts, oleosomes, and protein bodies. Consistent with this assumption, in spring sugar-Ps increased when phospholipids declined and poplar plants entering the vegetative growth period and, hence, metabolic activity increases. These results indicate that poplar trees adopt a policy of P nutrition without P storage and mobilization that is different from their N- and S-nutrition strategies.