Ground-level ozone differentially affects nitrogen acquisition and allocation in mature European beech (Fagus sylvatica) and Norway spruce (Picea abies) trees

Abstract

Impacts of elevated ground-level ozone (O(3)) on nitrogen (N) uptake and allocation were studied on mature European beech (Fagus sylvatica L.) and Norway spruce (Picea abies [L.] Karst.) in a forest stand, hypothesizing that: (i) chronically elevated O(3) limits nutrient uptake, and (ii) beech responds more sensitively to elevated O(3) than spruce, as previously found for juvenile trees. Tree canopies were exposed to twice-ambient O(3) concentrations (2 × O(3)) by a free-air fumigation system, with trees under ambient O(3) serving as control. After 5 years of O(3) fumigation, (15)NH(4)(15)NO(3) was applied to soil, and concentrations of newly acquired N (N(labelled)) and total N (N(total)) in plant compartments and soil measured. Under 2 × O(3), N(labelled) and N(total) were increased in the bulk soil and tended to be lower in fine and coarse roots of both species across the soil horizons, supporting hypothesis (i). N(labelled) was reduced in beech foliage by up to 60%, and by up to 50% in buds under 2 × O(3). Similarly, N(labelled) in stem bark and phloem was reduced. No such reduction was observed in spruce, reflecting a stronger effect on N acquisition in beech in accordance with hypothesis (ii). In spruce, 2 × O(3) tended to favour allocation of new N to foliage. N(labelled) in beech foliage correlated with cumulative seasonal transpiration, indicating impaired N acquisition was probably caused by reduced stomatal conductance and, hence, water transport under elevated O(3). Stimulated fine root growth under 2 × O(3) with a possible increase of below-ground N sink strength may also have accounted for lowered N allocation to above-ground organs. Reduced N uptake and altered allocation may enhance the use of stored N for growth, possibly affecting long-term stand nutrition.

Can needle nitrogen content explain the interspecific difference in ozone sensitivities of photosynthesis between Japanese larch (Larix kaempferi) and Sakhalin fir (Abies sachalinensis)?

“…Although there was no significant difference between the two species, the extent of NUE reduction was relatively higher in the fir than that in larch. The contrasting responses to O3 may be associated with the species-specific utilization of needle N. Larch, which has a deciduous leaf habit, exhibits a higher photosynthetic capacity and recycles N in needles before shedding, whereas evergreen conifers such as Sakhalin fir generally maintain needle N for relatively long periods (Millard and Proe 1992, Matsuda et al 2002, Weigt et al 2012. Evergreen conifer species also have lower NUE values to facilitate adaptation to resource-poor environments (Reich et al 1992(Reich et al , 1995 and they could drive sites toward resource-poor conditions by producing litter that does not easily decompose (Reich et al 1992).…”

“…It has also been reported that the thickness of the parenchyma cell layer is highly correlated with antioxidant capacity such as ascorbic acid-equivalent antioxidant capacity (Matyssek et al 2007(Matyssek et al , 2008. However, relatively few studies have compared O3 sensitivity between deciduous and evergreen trees based on LMA, particularly in coniferous species (Mortensen 1994, Wieser and Havranek 1996, Watanabe et al 2006, Weigt et al 2012.…”

“…A meta-analysis revealed that the mass-based relationship between photosynthesis and leaf N was always stronger than the area-based relationship (Wright et al 2004). In addition, deciduous and evergreen conifers are thought to have specific usages of needle N content, for example, photosynthetic N-use efficiency, leaf N cycling, and storage pools (Small 1972, Reich et al 1995, Temple et al 1995, Hikosaka 2004, Takashima et al 2004, Bussotti 2008, Weigt et al 2012. Particularly, N demand and turnover in deciduous trees are generally higher than that in evergreen trees (Matyssek 1986).…”

“…Conversely, Sakhalin fir has a lower photosynthetic capacity and exhibits high shade tolerance, which implies that it utilizes low levels of light, such as those available at the forest floor, more efficiently (Noguchi et al 2003). In addition, because the fir retains its evergreen needles for 5-10 years or more, depending on the light conditions, it can allocate N to needles, with N being continually recycled in some years until the light environment improves (Millard and Proe 1992, Noguchi et al 2003, Weigt et al 2012.…”

Elevated CO2 and O3 Levels Influence the Uptake and Leaf Concentration of Mineral N, P, K in Phyllostachys edulis (Carrière) J.Houz. and Oligostachyum lubricum (wen) King f.

“…In comparison, a few studies have investigated nutrient concentration and uptake in plants under elevated O 3 [26][27][28][29]. These studies have shown that the responses of plant N, P, and K concentrations and uptake to elevated O 3 are more complicated than responses to elevated CO 2 [28,30].…”