Influence of nitrogen fertilization on xylem traits and aquaporin expression in stems of hybrid poplar

Abstract

We studied the influence of nitrogen (N) on hydraulic traits and aquaporin (AQP) expression in the stem xylem of hybrid poplar saplings (Populus trichocarpa (Torr. & Gray) x deltoides Bartr. ex Marsh clone H11-11). Plants were grown in a controlled environment and were kept well watered throughout the experiments. Hydraulic measurements were done on basal and distal stem segments of plants receiving high N fertilization (high N plants) versus plants receiving only adequate N fertilization (adequate N plants). High N plants grew faster and exhibited more leaf area than adequate N controls. These morphological differences were paralleled by wider vessels and higher specific conductivities (K(S)) in high N plants. However, stems of high N plants were more vulnerable to xylem cavitation, at least in one of two experiments, and showed lower wood densities than stems of adequate N plants. Leaf area was strongly correlated with cross-sectional xylem area in both plant groups. Since higher K(S) in high N plants was accompanied by concomitant increases in leaf area, leaf-specific conductivities were similar in both plant groups. Influences of N on hydraulic traits were paralleled by changes in AQP expression. Seven AQPs were upregulated in the stem xylem of high N plants, five of which have been identified recently as water transporters. The enhanced growth of secondary xylem of high N plants has been shown to result from both increased cambial activity as well as increased cell size. We suggest that some of these water-transporting AQPs could play a role in xylogenesis, facilitating the influx of water into the zone of differentiating and maturing cells in secondary xylem, including expanding vessels.

Nutrient-Induced Modifications of Wood Anatomical Traits of Alchornea lojaensis (Euphorbiaceae)

“…This confirms observations for hybrid poplar, where an increase of N and/or P availability was reported to enhance vessel diameter in stems (Harvey and Van den Driessche, 1997;Hacke et al, 2010;Hacke, 2015). However, inverse responses of vessel diameter size after nutrient addition were also found (e.g., Arnold and Mauseth, 1999;Faustino et al, 2013).…”

“…However, studies focusing on nutrient-induced modification of wood anatomical traits are quite sparse (Harvey and Van den Driessche, 1997;Hacke et al, 2010;Hacke, 2015) and completely lacking in tropical regions at this time (Zuidema et al, 2013). But how can those changes of the vascular system be detected or calculated?…”

Allometric Equations for Estimating Compartment Biomass and Stem Volume in Mature Hybrid Poplars: General or Site-Specific?

“…This indicates that independently of the plantation site, the larger the trees of clone DN × M-915508 grow, the more water is contained in their freshly harvested bole biomass. Considering that the stem diameter of woody angiosperm is strongly and positively correlated with the diameter of water-transporting vessels [88], and that fertilization increases tree size and vessel diameter while decreasing wood density in hybrid poplar [87], our results support the idea that hybrid poplars of larger diameter have higher moisture content in their stems and lower basic density probably because they grew larger vessels.…”

“…Other studies done in southern Québec reported similar inter-site variation in stem basic density, but also lower basic density on higher fertility sites [39,40]. Similarly, Hacke et al [87] showed that the fertilization of hybrid poplars resulted in a decrease in wood density. In agreement with our hypotheses, the results also show that wood basic density is also size-dependent and tends to decrease with tree DBH (Figure 2a).…”

Sex-specific carbon and nitrogen partitioning under N deposition in Populus cathayana

“…Therefore, more and more N is being incorporated into the earth system. Many documents indicated that excess N not only affects tree architecture and vitality (Cooke et al 2005;Hacke et al 2010), but also impacts the dynamics, species richness, biodiversity, and functioning of ecosystems (Sala et al 2000;Stevens et al 2004;Phoenix et al 2006), because of accelerated soil acidification, reductions in the mineral elements essential for plant growth, and nutrient imbalances in plants (Magill et al 1997;Goulding et al 1998). Therefore, it is urgent to pay attention to the physiological and ecological differences among native species in response to N deposition, which could help to know the adaptive capability so as to predict its competition capacity and the shift of biodiversity when exposed to N deposition.…”