Root resorption completes the tree nitrogen economy: evidence from a 15-yr nitrogen addition experiment across stand ages.

Growth responses to climate warming and their physiological mechanisms differ between mature and young larch trees in a boreal permafrost region

SummaryArceuthobium sichuanense is a hemiparasitic angiosperm that infects Qinghai spruce (Picea crassifolia Kom.) in Qinghai province, China, and causes severe damage to spruce forests in Qinghai‐Tibet Plateau. In this study, the impact of A. sichuanense infection on mature and young trees of Qinghai spruce was evaluated by examining needle and current‐year shoot morphology, needle water and nitrogen‐use efficiency (NUE) and needle nitrogen concentration. The most apparent effect of A. sichuanense infection was a significant reduction in both needle size distal to infection and current‐year shoot length in the infected branches (p < 0.001). Per cent reductions in needle and current‐year shoot length were similar between mature and young trees (58.9 vs. 56.3%; 59.7 vs. 62.9%). There was a high degree of correlation in foliar δ15N values between the dwarf mistletoe and its host trees (R2 = 0.9017, p < 0.001), while the foliar δ13C values of A. sichuanense were similar to those of infected mature and young spruce trees. The dwarf mistletoe infection also resulted in a significant decrease in host needle N concentration and δ13C values (p < 0.001). The per cent reduction in needle N concentration in young trees was nearly twice as much as that in mature trees (20.49 vs. 11.54%), while the per cent reduction in needle δ13C values was similar between young and mature trees (−0.98 vs.−1.1‰). The NUE in mature trees was not affected by A. sichuanense infection, but the NUE in young trees was increased by the infection.

Severity of Swiss needle cast in young and mature Douglas-fir forests in western Oregon, USA

The impact of mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytinae), is the most significant source of mortality of mature pine forests in western North America; however, in 2003-2004, high levels of mortality were observed in young pine stands in central British Columbia. This study investigagtes the impact of mountain pine beetle in these young pine stands. In 2005 and 2006, 24 plots were established throughout the mountain pine beetle-affected area of British Columbia. Cumulative mortality reached 83% in some plots. Secondary bark beetles and other pests contributed to overall stand mortality and decline but to a far lesser degree than mountain pine beetle. Stem deterioration and falldown was very rapid and severe in young stands following attack. Over 70% of attacked trees in the Sub-Boreal Spruce ecosystem were severely deteriorated, or had fallen less than 5 years after attack. The largest pines in young stands were attacked first, and brood production and emergence in these trees was more successful than in smaller, younger cohorts. Many attached stands had received silvicultural treatments. Once the outbreak in adjacent mature stands had subsided, very little new attack occurred in these young stands. Brood production was successful, albeit lower in young trees than in mature trees.

Populations of Sharpshooters in Two Citrus Groves in East-central Florida as Indicated by Yellow Sticky Card Traps

This thesis is subdivided into two main research areas. The first two studies were conducted in a mature mixed temperate broad leaved forest with regard to species identity effects on fine root traits, while the third study of the thesis addresses the influence of soil temperature on fine roots of Pinus cembra at the alpine treeline. In the species-rich broad leaved forest within the Hainich National Park, we assessed the role of taxonomic position and mycorrhiza type (EM and AM) on fine root biomass, fine root morphology (on root order level) and fine root dynamics of six coexisting tree species (Fagus sylvatica L., Tilia cordata Mill., Carpinus betulus L., Fraxinus excelsior L., Acer pseudoplatanus L. Acer platanoides L.). We detected similar trends of a decrease of specific root area and specific root length from the first (the root tips) to the fourth root order in all six species. Nevertheless, the root order traits differed strongly between the species, especially for the variables root tissue density and root nitrogen concentration. The highest root nitrogen contents were found in the root tips and decreased with root order. Comparing the species, F. excelsior contained the highest nitrogen content in all root orders. Fine root productivity differed strongly between the six species with the highest production in C. betulus, F. sylvatica, and F. excelsior (~ 150-170 g m-2 yr-1). Most differences in fine root production and turnover between the species were found in the deeper soil layers compared to the upper soil layer at 0-10 cm. Root turnover varied up to fivefold among the species, with lowest values in Acer pseudoplatanus and highest values in its congener A. platanoides. Even these two congeneric species differed strongly in their branching traits in the same stand, suggesting that they use differing belowground foraging strategies (e.g. more root tips per biomass in A. pseudoplatanus vs. a higher root turnover in A. platanoides). In general, species identity was found to be the most important determining factor for fine root morphology and biomass as well as for fine root productivity and turnover rates, whereas the influence of mycorrhiza type was only of secondary importance. Species differences in fine root traits were more pronounced for the respective root orders than in comparison for the whole root branches. At the alpine treeline, soil temperature is assumed to be the key factor influencing root biomass, production and morphology of fine roots. So far, most studies have been conducted on temperature influences on fine roots of tree saplings and juvenile trees in ex-situ experiments, and there is very little data on temperature dependent fine root traits of mature trees at the treeline. In this study we investigated fine root mass distribution, fine root morphology and fine root production and turnover around solitary Pinus cembra trees at the alpine treeline in the Central Eastern Alps in Austria. Those fine root data were linked to soil temperatures around the trees, measured at the time with maximal temperature deviations between shade and sun. The main objective was to determine whether soil temperature, lowered by the shade of the crown, impairs fine root growth around mature Pine trees. In contrast to previous findings regarding fine root reactions to low temperatures, we found higher fine root masses (living and dead) in cooler areas around the tree stems during a sunny summer day. Additionally in cooler, shaded soil there was a higher fine root production and turnover, which leads us to the assumption that trees invest more carbon into fine roots of cooler soil areas to compensate fine root loss and maintain optimal resource acquisition, as nutrient accessibility is lower in cold soil areas. In general, our findings suggest that fine root traits and their dependency of soil temperatures might not be comparable between tree saplings and mature trees.

The nutritive value of <i>Acacia saligna</i> and <i>Acacia salicina</i> for goats and sheep

High soil acidity and elevated soil Al concentrations limit plant growth in many terrestrial ecosystems. Aluminium toxicity can be ameliorated by Ca. Thus, Ca/Al molar ratios in soil solution and in plant tissues have been proposed as superior indicators than Al concentration itself for evaluating the Al toxicity stress to trees (Cronan & Grigal, J Environ Qual 1995;24:209 – 226). This article presents an overview of publications since 1995 where the reduced Ca/Al ratio in fine tree roots has been used as an indicator of stress for Al and/or soil acidity. The main aim of this review was to evaluate the use and the critical threshold of the fine root Ca/Al ratio as a potential indicator for Al toxicity stress to trees in acid soils. Based on the reviewed literature, the fine root Ca/Al molar ratio was strongly negatively related to Al stress in small tree seedlings in controlled environments, whereas the response was not clear under field conditions where other environmental factors interact. Fine root Ca/Al ranged from 0.03 to 17 in tree seedlings and from 0.1 to 18 in mature trees depending on experimental and site conditions, as well as the tolerance and uptake mechanisms of the different tree species. Fine root Ca/Al was positively related to the soil solution Ca/Al molar ratio. Fine root Ca/Al ratios were related positively to fine root length, growth, specific root length, and biomass, and negatively to root diameter, callose formation, respiration chain activity, starch concentration, and root necromass. A number of relationships have been also found between the fine root Ca/Al and above-ground seedling and/or mature tree growth and nutrient uptake. The critical thresholds for the Ca/Al fine root ratio of 0.2 suggested by Cronan and Grigal (1995) is estimated to represent 90% risk of inverse impact on root and above-ground tree growth. Values of Ca/Al molar ratio in the fine roots of mature trees were only rarely determined below the critical 0.2. The caveats for the use and the interpretation of Ca/Al ratio in fine roots have been addressed in detail. A protocol for root processing and elemental analysis to obtain reliable and comparable results of Ca and Al concentrations in roots is also provided. The article concludes with recommendations for a wider use of the Ca/Al ratio in roots as a bioindicator of Al toxicity to trees in acid soils.

Summary Optimal resource partitioning theory predicts that plants should increase the ratio between water absorbing and transpiring surfaces under short water supply. An increase in fine root mass and surface area relative to leaf area has frequently been found in herbaceous plants, but supporting evidence from mature trees is scarce and several results are contradictory. In 12 mature Fagus sylvatica forests across a precipitation gradient (820–540 mm yr−1), we tested several predictions of the theory by analysing the dependence of standing fine root biomass, fine root production and fine root morphology on mean annual precipitation (MAP), the precipitation of the study year, and stand structural and edaphic variables. The water storage capacity of the soil (WSC) was included as a covariable by comparing pairs of stands on sandy (lower WSC) and loam‐richer soils (higher WSC). Fine root biomass, total fine root surface area, fine root production and the fine root : leaf biomass production ratio markedly increased with reduced MAP and precipitation in the study year, while WSC was only a secondary factor and stand structure had no effect. The precipitation effect on fine root biomass and production was more pronounced in stands on sandy soil with lower WSC, which had, at equal precipitation, a higher fine root biomass and productivity than stands on loam‐richer soil. The high degree of allocational plasticity in mature F. sylvatica trees contrasts with a low morphological plasticity of the fine roots. On the more extreme sandy soils, a significant decrease in mean fine root diameter and increase in specific root area with decreasing precipitation were found; a similar effect was absent on the loam‐richer soils. Synthesis. In support of optimal partitioning theory, mature Fagus sylvatica trees showed a remarkable allocational plasticity as a long‐term response to significant precipitation reduction with a large increase in the size and productivity of the fine root system, while only minor adaptive modifications occurred in root morphology. More severe summer droughts in a future warmer climate may substantially alter the above‐/below‐ground C partitioning of this tree species with major implications for the forest C cycle.

SummaryChanges in the nutrient content of oranges from young and mature ‘Bellamy’ navel orange trees were measured throughout fruit development. Calculated net influxes of the macronutrients, K, Ca, Mg, P and S, and the micronutrients, Fe, B, Zn, Mn and Cu increased during Stage I of fruit development and reached a maximum 8–10 weeks after flowering (ca. two weeks after the end of Stage I). There was little temporal variation of flux maxima between fruit from young and mature trees, but flux maxima were higher for most nutrients in fruit from mature trees compared with fruit from young trees. During early growth (fruit dry weight <10.g) the contents of K and B (phloem mobile), and of Ca and Cu (phloem immobile) increased linearly in relationship to fruit dry weight. In contrast to K and B, the Ca and Cu content plateaued at a fruit dry weight of 15.g. During Stage I of fruit development the K influx, normalized to fruit dry weight, was the same in fruit from young and mature trees but the normalized Ca flux was higher in fruit from young trees than from mature trees. There was comparatively greater influx of Ca into the albedo than the pulp during Stage I of fruit development. During Stage I of fruit development, normalized Ca fluxes into whole fruit and albedo tissue were higher in fruit from young trees than in fruit from mature trees. The latter have a history of high incidence of rind crease. The results are discussed in relation to the relative mobility of nutrients in phloem and xylem during fruit growth.

Seasonal ozone response of mature beech trees (Fagus sylvatica) at high altitude in the Bavarian forest (Germany) in comparison with young beech grown in the field and in phytotrons

Does stoichiometric homeostasis differ among tree organs and with tree age?

Hydraulic specific conductivity, vulnerability to cavitation and water storage capacity of Douglas-fir sapwood was determined for samples from six young (1.0–1.5 m tall) and six mature trees (41–45 m tall). Measurements on samples from young trees showedthere were no effects of two contrasting sample types (entire stem segments vs sectors chiseled out of entire stems) on any of the calculated hydraulic parameters, for vulnerability to cavitation and water storage capacity. Measurements on mature trees were made on wood from four heights on the bole and from two sapwood depths. Outer and inner sapwood at the base of the tree had higher water storage capacities and were more vulnerable to cavitation than was sapwood from the tree top. At every height, old trees were more vulnerable to cavitation than at 1.0 m from the ground in young trees. The water storage capacities showed three distinct phases at the base of the trunk. Young trees had similar water storage capacity (per unit volume of sapwood) to the topof the mature trees, which was lower than the water storage capacity throughout the rest of the bole xylem. The way in which capacitance was calculated (on a volumetric basis vs a relative water content basis) affected the conclusion one would draw at the low water potentials (<–3 MPa). Within a tree, we found an apparent trade-off between having both hydraulic specific conductivity and stem water storage, and vulnerability to cavitation.

The potential contribution of mycorrhizal fungi (as sporocarps and mycorrhizal sheaths) to total ecosystem biomass and turnover and nutrient distribution and turnover was examined in a 23—yr—old and a 180—yr—old Pacific silver fir (Abies amabillis) stand in western Washington. While mycorrhizal fungi contributed roughly 1% a total ecosystem biomass in both stands, the percentage of net primary production (NPP) in the mycorrhizal fungal component was roughly 14% in the younger stand and 15% in the mature stand. Mycorrhizal fungi plus conifer fine roots contributed °45% of NPP in the young stand and °75% in the mature stand. Sclerotia production (2700 kg°ha—1°yr—1) contributed the largest proportion of total mycorrhizal fungal production in both stands followed by mycorrhizal sheath production (°350 kg°ha—1°yr—1 and 430 kg°ha—1°yr—1 in the young and mature stands, respectively). Potentially, 27 kg°ha—1°yr—1 of N is cycled through sporocarps in the young stands and 41 kg°ha—1°yr—1 in the mature stand. Annually, fine roots (including mycorrhizae) cycle at least 60, 10, 20, 30 and 10 kg°ha—1°yr—1 of N, P, K, Ca, and Mg, respectively, in the young stand. In contrast, 110, 20, 20, 30 and 10 kg°ha—1°yr—1 of N, P, K, Ca and Mg, respectively, are cycled through fine roots in the mature stand.

Growth intensity of particular tree components is controlled by a variety of factors and as a consequence, biomass allocation also changes over time. Since the allocation of biomass controls the carbon regime in a forest stand, tree standing stock and biomass structure, with regard to tree components: fine and coarse roots, stem, branches and needles, were estimated in a young Norway spruce stand based on repeated tree sampling, soil coring and allometric equations (modelled for 2009 and 2013, i.e. for 12- and 16-years-old trees). Large differences were found between the two models in the contribution of the tree components to aboveground biomass. Between the first and fifth year of the experiment, below - ground to aboveground biomass ratio as well as short-lived to long-lived tree part ratio manifested decreasing tendencies. At the same time, the stand possibly reached the maximum standing stock of both needles and fine roots. It is concluded that for biomass allocation estimates in young stands, not only stand-specific but also time-specific allometric relations should be constructed and implemented. Further, there appears to be a canopy closure threshold beyond which biomass allocation is different from the situation in sparse young spruce stands.