Morphological Response of Jack Pine to the Interactive Effects of Carbon Dioxide, Soil Temperature and Photoperiod

Responding to the predicted shift in climate envelope jack pine, (Pinus banksiana Lamb.) might migrate 10° northward between 2071 and 2100 and will be exposed to a different photoperiod regime. Successful migration of the species might depend on the initial acclimating capability to the conditions of new location. The impacts of elevated carbon dioxide concentration [CO2], soil temperature and photoperiod on the phenological traits, growth and biomass responses in jack pine seedlings were investigated. Seedlings were grown in greenhouses under two [CO2] (400 and 950 μmol•mol-1), two soil temperatures (ambient soil temperature at seed origin and 5°C warmer) and three photoperiod regimes (photoperiods at seed origin, 5° north of the seed origin and 10° north of the seed origin). Budburst and bud setting time were recorded and the seedling height (Ht), root collar diameter (RCD), root biomass, stem biomass and leaf biomass were measured after six months of treatment. It was observed that under elevated [CO2], ambient Tsoil and photoperiods associated with 10° northward migrations budburstis advanced by 10 days. Photoperiods toward north significantly prolonged the bud setting time. However, tri-factor interactive effect on bud set was not statistically significant. Elevated [CO2] significantly (P < 0.05) increased the RCD, volume of the seedlings and total biomass and longer growing season photoperiods towards north significantly increased the seedling heights. Though elevated [CO2] significantly increased the projected leaf area, it had no significant effect on specific leaf area. Elevated [CO2] significantly reduced the shoot to root ratio, which indicated higher biomass allocation in roots under elevated [CO2]. However, all these growth and biomass responses were statistically insignificant under tri-factor interactive effects. The results suggest that climate change induced northward migration will not affect the growth of jack pine. However, a long distance migration (e.g. 10° north) will expose the species to late-spring frost damage.

N/P/K Ratios and CO₂Concentration Change Nitrogen-Photosynthesis Relationships in Black Spruce

The relationship between photosynthesis and leaf nitrogen concentration is often used to model forest carbon fixation and ratios of different nutrient elements can modify this relationship. However, the effects of nutrient ratios on this important relationship are generally not well understood. To investigate whether N/P/K ratios and CO2 concentration ([CO2]) influence relationships between photosynthesis and nitrogen, we exposed one-year-old black spruce seedlings to two [CO2] (370 and 720 μmol·mol-1), two N/P/K ratio regimes (constant (CNR) and variable (VNR) nutrient ratio) at 6 N supply levels (10 to 360 μmol·mol-1). It was found that photosynthesis (Pn) was more sensitive to nitrogen supply and N/P/K ratios under the elevated [CO2] than under ambient [CO2];under the elevated [CO2], Pn declined with increases in N supplies above 150 μmol·mol-1 in the CNR treatment but was relatively insensitive to N supplies of the same range in the VNR treatment. Further, our data suggest that the nutrient ratio and the CO2 elevation effects on photosynthesis were via their effects on the maximum rate of carboxylation (Vcmax) but not electron transport (Jmax) or triose phosphate utilization (TPU). The results suggest that the CO2 elevation increased the demand for all three nutrient elements but the increase was greater for N than for P and K. The CO2 elevation resulted in greater photosynthetic use efficiencies of N, P and K, but the increases varied with the nutrient ratio treatments. The results suggest that under elevated [CO2], higher net photosynthetic rates demand different optimal N-P-K ratios than under the current [CO2].

Soil Temperature and Phosphorus Supply Interactively Affect Physiological Responses of White Birch to CO₂Elevation

Phosphorus (P) is a common limiting nutrient element to plants and its supply and uptake by plants are strongly influenced by soil temperature. However, the interactive effects of the two factors on the physiological responses of plants to global change are poorly understood. In this study, we examined how P supply and Tsoil interacted in affecting physiological responses in white birch (Betula papyrifera) to [CO2]. We exposed seedlings to 7°C, 17°C and 27°C Tsoil, 0.1479, 0.3029 and 0.5847 mM P2O5, and 360 and 720 μmol·mol-1 [CO2] for four months. We have found that both the low soil temperature and CO2 elevation resulted in photosynthetic down regulation but the specific mechanisms of the down regulation were different between the two treatments, particularly the relative contributions of biochemical and photochemical capacity, mesophyll conductance and sink strength for carbohydrate utilization to the down regulation. Furthermore, our data suggest that morphological adjustments, such as reduced leaf size and total leaf area, were the primary form of responses in white birch to low phosphorus supply and no significant physiological acclimation to P supply was detected. Our results suggest that white birch will likely enhance water use efficiency under the projected future climate conditions with doubled carbon dioxide concentration, particularly at warmer soil temperatures. Although a trade-off between water use efficiency and nutrient use efficiency is widely accepted, our results suggest that there does not have to be a trade-off between the two, for instance, CO2 elevation increased both use efficiencies and low soil temperature and reduced nitrogen efficiency without affecting water use efficiency under elevated CO2.

Photoperiod and Nitrogen Supply Limit the Scope of Northward Migration and Seed Transfer of Black Spruce in a Future Climate Associated with Doubled Atmospheric CO2 Concentration

The predicated changes in precipitation and temperature associated with the continued elevation of atmospheric CO2 concentration will trigger the northward shift of the Climate Envelopes for 130 North America tree species by as much as 10 degrees. However, climate envelope models do not take into account changes in other factors that may also influence the survival and growth of plants at the predicted new locations, such as photoperiod and nutrient regimes. This study investigated how photoperiod and nitrogen supply would affect the ecophysiological traits of black spruce (Picea mariana (Mill) B. S. P.) that are critical for survival and growth at new locations predicted by climate envelope models. We exposed black spruce seedlings to the photoperiod regime at the seed origin (PS) and that 10° north of the seed origin (PNM) as predicted by climate envelope models under the current and doubled atmospheric CO2 concentration and different levels of N supply (30 vs. 300 μmol·mol-1 N). We found that the PNM and the 30 μmol·mol-1 N supply both had negative impact on the development of seedling cold hardiness in the fall, and led to earlier burst of the terminal bud and greater rate of mortality in the following growing season. While the PNM stimulated seedling growth in the first growing season, the effect was not sustained in the second growing season. Our results suggest that the photoperiod regimes and poor nutrient conditions at higher latitudes will likely constrain the scope of the northward migration or seed transfer of black spruce.

Effects of elevated carbon dioxide concentration and soil temperature on the growth and biomass responses of mountain maple (Acer spicatum) seedlings to light availability

Aims Some shade-tolerant understory tree species such as mountain maple(Acer spicatum L.)exhibit light-foraging growth habits.Changes in environmental conditions,such as the rise of carbon dioxide concentration([CO_(2)])in the atmosphere and soil warming,may affect the performance of these species under different light environments.We investigated how elevated[CO_(2)]and soil warm-ing influence the growth and biomass responses of mountain maple seedlings to light availability.Methods The treatments were two levels of light(100%and 30%of the ambient light in the greenhouse),two[CO_(2)](392μmol mol^(−1)(ambient)and 784μmol mol^(−1)(elevated))and two soil tempera-tures(Tsoil)(17 and 22℃).After one growing season,we measured seedling height,root collar diameter,leaf biomass,stem biomass and root biomass.Important findings We found that under the ambient[CO_(2)],the high-light level increased seedlings height by 70%and 56%at the low Tsoil and high Tsoil,respectively.Under the elevated[CO_(2)],however,the high-light level increased seedling height by 52%and 13%at the low Tsoil and high Tsoil,respectively.The responses of biomasses to light generally followed the response patterns of height growth under both[CO_(2)]and Tsoil and the magnitude of biomass response to light was the lowest under the elevated[CO_(2)]and warmer Tsoil.The results suggest that the elevated[CO_(2)]and warmer Tsoil under the projected future climate may have negative impact on the colonization of open sites and forest canopy gaps by mountain maple.

北方针叶树CO_(2)的刺激和响应机制随光强而变化

黑云杉(Picea mariana[Mill.]B.S.P.)和白云杉(Picea glauca[Moench]Voss.)是同属物种,两者都是适度耐阴,并且在北美北方针叶林中广泛分布。为了了解光照对CO_(2)浓度升高的生理生态反应的影响,在三种光照条件下(温室中光照设置为100%、50%和30%)将一年生的两种幼苗暴露在360和720µmol mol–1浓度的CO_(2)环境中,测定了其中后期叶面气体交换量。研究结果表明,CO_(2)的浓度升高提高了净光合速率(Pn)和光合水分利用效率,但降低了气孔导度和蒸腾作用。CO_(2)对光合作用的刺激在50%光照下最大,在100%光照下最小。光合作用、最大羧化速率(Vcmax)和光饱和电子传递速率(Jmax)均随光照强度的降低而降低。升高的CO_(2)在所有光照处理中显著降低了Vcmax,在生长季节中期,两种云杉的Vcmax均显著降低,但在生长季节后期,当光照达到30%时,这一影响变得不明显,而且黑云杉的响应大于白云杉。CO_(2)浓度升高也降低了白云杉的Jmax,但在生长季后期30%光照时,这种影响变得不显著。但CO_(2)浓度升高对黑云杉的影响随时间而变化。在所有光照处理中,CO_(2)浓度升高降低了黑云杉生长中期的Jmax,且在生长后期30%光照时影响不显著,但在100%和50%光照时,Jmax升高。这些研究结果表明,两个树种植物都受益于CO_(2)浓度的升高,但它们的响应机制随着光照的增加而变化:即在100%和50%光照下,它们的响应主要是生理上的,而在30%光照下,它们的响应主要是形态上的。

Biochar and alternate partial root-zone irrigation greatly enhance the effectiveness of mulberry in remediating lead-contaminated soils

土壤铅污染日益严重,植物修复是一种环保的污染土壤修复技术。本文旨在研究四种土壤铅污染水平下,添加生物碳和分根区交替灌溉(Alternative Partial Root-zone Irrigation,APRI)对桑树幼苗的生长、铅适应性和铅积累的影响。我们以生物碳(添加与不添加生物碳)、灌溉方式(APRI与常规灌溉)和土壤铅水平(0、50、200和800 mg kg^(-1) Pb)为三因素实施了温室试验。通过测定桑树幼苗的生长性状、渗透物质代谢、抗氧化酶活性、铅的积累和转运等参数,探讨了不同处理对桑树生长发育的影响。结果表明,桑树对土壤铅污染有较强的适应能力;生物碳和APRI在不同土壤铅水平上协同提高了生物量和吸收根表面积。桑树通过调节谷胱甘肽(GSH)、脯氨酸代谢和过氧化物酶(POD)活性,增加了渗透和抗氧化调节能力,进而提高了对重度铅污染土壤(800 mg kg^(-1))的抗性。桑苗中的铅离子主要集中在根中,与土壤铅浓度具有剂量效应。土壤铅、生物碳和ARPI的交互作用影响了叶片和根系中铅的浓度、转运和生物富集系数。综上所述,在桑树栽培中结合外源生物碳和APRI可有效地用于修复土壤铅污染。