Carbon allocation, nodulation, and biological nitrogen fixation of black locust (Robinia pseudoacacia L.) under soil water limitation

Abstract

. Carbon allocation, nodulation, and biological nitrogen fixation of black locust (Robinia pseudoacacia L.) under soil water limitation. Ann. For. Res. 58(2): 259-274.Abstract. The pioneer tree black locust (Robinia pseudoacacia L.) is a drought-resistant tree and, in symbiosis with Rhizobium, able to fix dinitrogen from the atmosphere. It is, therefore, an interesting species for marginal lands where soil amelioration is sought in addition to economic gain. However, the interaction between soil water availability, carbon allocation and nitrogen fixation is important for a successful establishment of trees on marginal lands and has not yet been investigated for black locust. Twoyear-old trees were grown under various soil water conditions and drought cycles. The stable isotopic composition of C (δ 13 C) and N (δ 15 N) of the leaves was used to identify i) the effective drought condition of the treatments and ii) the portion N accrued from the atmosphere by the biological nitrogen fixation. Drought-stressed plants significantly reduced their total aboveground biomass production, which was linearly linked to tree transpiration. The shoot:root ratio values changed from 2.2 for the drought-stressed to 4.3 for the well-watered plants. Our investigation shows that drought stress increases the nodule biomass of black locust in order to maintain biological nitrogen fixation and to counteract the lower soil nitrogen availability. The biological nitrogen fixation of drought-stressed trees could be maintained at relatively higher values compared to the well-watered trees. The average leaf nitrogen content varied between 2.8% and 3.0% and was not influenced by the drought stress. Carbon fixation, carbon allocation, and biological nitrogen fixation are to some extent balanced at low irrigation and allow Robinia to cope with long-term water constraints. The combination of black locust's ecophysiological and morphological plasticity make it interesting as a biomass source for bioenergy and timber production, even in nutrient-limited and drought-affected areas of Europe.

Estimating symbiotic N2 fixation in Robinia pseudoacacia

“…In our study, up to 76% of the N in the black locust standing biomass came from atmospheric N 2 fixation, representing N inputs ranging between 5.7 and 12.5 kg N ha −1 y −1 . Similar Ndfa values were found by Mantovani et al () for young black locust trees. This reflects a total N amount fixed of 45.4 kg N ha −1 almost 5 years after planting, when litter fall is taken into account.…”

Drought sensitivity of an N2‐fixing tree may slow temperate deciduous forest recovery from disturbance

“…If stomatal limitation due to soil moisture deficit reduces the potential C gain from photosynthesis, the primary use of N, then there is less benefit from acquiring additional N. Although we did not observe significant changes in instantaneous measures of stomatal conductance for any species, we found that long-term water-use efficiency (d 13 C) increased for R. pseudoacacia and Q. velutina, but not L. tulipifera or A. rubrum, with declining soil moisture. This trend is consistent with prior evidence that R. pseudoacacia reduces stomatal conductance and increases its wateruse efficiency under dry conditions (Wurzburger and Miniat 2014, Mantovani et al 2015, Minucci et al 2017. Additionally, we found that low moisture was associated with a decline in foliar N concentration of R. pseudoacacia, but not nonfixing species, supporting the idea that reductions in SNF (due to its lower marginal benefit) may explain the reduced competitive ability of R. pseudoacacia.…”

“…Synthesis of individual and community-level responses to declining soil moisture. This trend is consistent with prior evidence that R. pseudoacacia reduces stomatal conductance and increases its wateruse efficiency under dry conditions (Wurzburger and Miniat 2014, Mantovani et al 2015, Minucci et al 2017. In each box, leaves are ordered from left to right (Robinia pseudoacacia, Quercus velutina, Acer rubrum, and Liriodendron tulipifera).…”

Drought Decreases Growth and Increases Mortality of Coexisting Native and Introduced Tree Species in a Temperate Floodplain Forest

“…In black locust, reductions in soil water availability decrease growth and photosynthate availability, promote leaf shedding, and negatively affect N-fixing bacteria by reducing nodule biomass, leading to tree death in some cases [69][70][71]. Nevertheless, greenhouse experiments based on seedlings have showed that moderate droughts exacerbate soil N deficiency but increase the biomass of nodules, thus benefitting the black locust over non-fixing tree species [72].…”