The responses of Scots pine seedlings to waterlogging during the growing season (original) (raw)
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The responses of Scots pine seedlings to waterlogging during growing season
Canadian Journal of Forest Research, 2016
In the future management and sustainable use of boreal forests, it is crucial to consider the rate and strength of tree responses to an elevated water table and the concurrent oxygen limitations, especially in peatlands. We examined the response dynamics of 7-year-old Scots pine (Pinus sylvestris L.) seedlings to a 5-week waterlogging (WL) treatment during a growing season in a root lab (dasotron) experiment. WL took place after shoot elongation had ended but while growth of the trunk diameter was still in progress. Trunk sap flow and needle water potential started to decrease immediately after the onset of WL, while the first signs in needle gas exchange — seen as decreases in the potential efficiency of photosystem II, the rates of light-saturated net assimilation and transpiration, and increased needle respiration — were observed after 3 weeks of WL. New needles responded to WL more strongly than the old ones. Drainage with consequent re-oxygenation of the soil caused a further d...
Tree Physiology, 2020
Future climate scenarios for the boreal zone project increasing temperatures and precipitation, as well as extreme weather events such as heavy rain during the growing season. This can result in more frequent short-term waterlogging (WL) leading to unfavorable conditions for tree roots. In addition, it is decisive whether short-term WL periods during the growing season occur continuously or periodically. We assessed the effects of short-termed WL on 4-year-old Scots pine (Pinus sylvestris L.) saplings after shoot elongation started. Waterlogging (WL) lasted either continuously for 2.5 weeks (ContWL) or noncontinuously for 5 weeks, consisting of three repeated 1-week-interval WL periods (IntWL). Both treatments resulted in the same duration of soil anoxia. We studied soil gases, root and shoot growth and physiology, and root survival probability and longevity during the experiment. In the final harvest, we determined shoot and root biomass and hydraulic conductance and electrical impedance spectra of the root systems. Soil CO 2 and CH 4 concentrations increased immediately after WL onset and O 2 decreased until anoxia. Waterlogging decreased fine root survival probability, but there was no difference between WL treatments. Shoot growth suffered more from ContWL and root growth more from IntWL. Needle concentrations of pinitol increased in the WL saplings, indicating stress. No WL effects were observed in photosynthesis and chlorophyll fluorescence. Increased starch concentration in needles by WL may be due to damaged roots and thus a missing belowground sink. Electrical impedance indicated suffering of WL saplings, although root hydraulic conductance did not differ between the treatments. Oxidative stress of short-term and interval WL can have long-lasting effects on shoot and root growth and the physiology of Scots pine. We conclude that even short-term WL during the growing season is a stress factor, which will probably increase in the future and can affect carbon allocation and dynamics in boreal forests.
Forest Ecology and Management, 2013
Depending on the soil preparation method applied and peat characteristics, Scots pine (Pinus sylvestris L.) seedlings planted in prepared spots on forestry-drained peatlands may become more susceptible to extreme weather events such as drought or flooding. Only by studying its coping strategies can we eventually design methodology better suited for Scots pine regeneration on peat soils. In this study, we evaluated the tolerance of two-year-old seedlings to the two extremes of water-associated stress, drought and waterlogging, in unprocessed peat. Over one growing season in controlled conditions, drought distinctly reduced root and shoot growth in addition to photochemical efficiency (F v /F m ) particularly in previous-year needles, whilst wet stress had little discernible impact. Drought also influenced polyamine metabolism by increasing free putrescine and spermine concentrations especially in current-year needles, whereas no impact was discerned in the wet treatment. Furthermore, reduced root hydraulic conductance (K r ) was observed in drought-stressed root systems. Apparently, waterlogging does not modify Scots pine seedling growth or vitality immediately, but rather in the longer term. However, no fatalities occurred in either of the stress treatments, this despite water availability in the Sphagnum peat reaching its lower (permanent wilting point) and upper (10% soil air content) limits. Maintenance of rather high photochemical efficiency despite severe drought stress would seem to indicate a potential for seedling recovery if water availability in the peat substrate improved.
Canadian Journal of Forest Research
Excess water in the rooting zone critically reduces tree growth and may even kill trees; however, the relative importance of damage to roots versus aboveground parts and the time course of damage are not well understood. We studied the dynamics of fine-root growth and mortality of 7-year-old Scots pine (Pinus sylvestris L.) saplings affected by a 5-week period of waterlogging (WL) during the growing season. Two out of six WL-exposed saplings survived the treatment. After 1–2 weeks of WL, the mortality of the first-order short roots (usually mycorrhizas) started to increase and the production of these roots started to decrease. WL decreased the longevity of short and long roots. Total root length (especially of fine roots with a diameter < 0.5 mm), specific fine-root length, total root dry mass (including stump), and reverse-flow root hydraulic conductance were lower in WL saplings than in control saplings at the end of the experiment; however, several root traits were similar in ...
Tree Physiology, 1996
Effects of needle water potential (Ψ l) on gas exchange of Scots pine (Pinus sylvestris L.) grown for 4 years in open-top chambers with elevated temperature (ET), elevated CO 2 (EC) or a combination of elevated temperature and CO 2 (EC + ET) were examined at a high photon flux density (PPFD), saturated leaf to air water vapor pressure deficit (VPD) and optimal temperature (T). We used the Farquhar model of photosynthesis to estimate the separate effects of Ψ l and the treatments on maximum carboxylation efficiency (V c,max), ribulose-1,5-bisphosphate regeneration capacity (J), rate of respiration in the light (R d), intercellular partial pressure of CO 2 (C i) and stomatal conductance (G s). Depression of CO 2 assimilation rate at low Ψ l was the result of both stomatal and non-stomatal limitations on photosynthetic processes; however, stomatal limitations dominated during short-term water stress (Ψ l < −1.2 MPa), whereas nonstomatal limitations dominated during severe water stress. Among the nonstomatal components, the decrease in J contributed more to the decline in photosynthesis than the decrease in V c,max. Long-term elevation of CO 2 and temperature led to differences in the maximum values of the parameters, the threshold values of Ψ l and the sensitivity of the parameters to decreasing Ψ l. The CO 2 treatment decreased the maximum values of V c,max , J and R d but significantly increased the sensitivity of V c,max , J and R d to decreasing Ψ l (P < 0.05). The effects of the ET and EC + ET treatments on V c,max , J and R d were opposite to the effects of the EC treatment on these parameters. The values of G s , which were measured simultaneously with maximum net rate of assimilation (A max), declined in a curvilinear fashion as Ψ l decreased. Both the EC + ET and ET treatments significantly decreased the sensitivity of G s to decreasing Ψ l. We conclude that, in the future, acclimation to increased atmospheric CO 2 and temperature could increase the tolerance of Scots pine to water stress.
Tree Physiology
We investigated the impact of drought on the physiology of 41-year-old Scots pine (Pinus sylvestris L.) in central Scotland. Measurements were made of the seasonal course of transpiration, canopy stomatal conductance, needle water potential, xylem water content, soil-to-needle hydraulic resistance, and growth. Comparison was made between drought-treated plots and those receiving average precipitation. In response to drought, transpiration rate declined once volumetric water content (VWC) over the top 20 cm of soil reached a threshold value of 12%. Thereafter, transpiration was a near linear function of soil water content. As the soil water deficit developed, the hydraulic resistance between soil and needles increased by a factor of three as predawn needle water potential declined from −0.54 to −0.71 MPa. A small but significant increase in xylem embolism was detected in 1-year-old shoots. Stomatal control of transpiration prevented needle water potential from declining below −1.5 MPa. Basal area, and shoot and needle growth were significantly reduced in the drought treatment. In the year following the drought, canopy stomatal conductance and soil-to-needle hydraulic resistance recovered. Current-year needle extension recovered, but a significant reduction in basal area increment was evident one year after the drought. The results suggest that, in response to soil water deficit, mature Scots pine closes its stomata sufficiently to prevent the development of substantial xylem embolism. Reduced growth in the year after a severe soil water deficit is most likely to be the result of reduced assimilation in the year of the drought, rather than to any residual embolism carried over from one year to the next.
Annales des Sciences Forestières, 1994
Seedlings of Quercus robur, Q rubra and Fagus silvatica were submitted to a period of partial (water table at 6 cm below ground) or total water-logging for 4 weeks. Important disorders were induced by the latter treatment in growth (root decay, partial leaf wilting), water relations (decreased predawn water potential) and photosynthesis (stomatal closure, reduced net assimilation rates, lowered O 2 evolution under saturating CO 2 and irradiance, and limited photochemical efficiency of PS II). It has been concluded that the observed stomatal closure was accompanied by strong disorders at chloroplast level, which happened without visible waterlogging-induced deficiencies in mineral nutrient supply. Reactions to partial water-logging were much more limited. F silvatica displayed the strongest disorders in response to both treatments, Q robur showed only slight stress effects in response to partial water-logging and Q rubra had intermediate behaviour. These observations are in agreement with the reported differences in sensitivity to water-logging of adult trees in the stand. The precise chain of events leading to these disorders in the shoots of waterlogged seedlings remains to be elucidated. stomatal conductance / hydraulic conductance / mineral nutrition / photochemistry / photosystem II Abbreviations. ψ wm and ψ wα : midday and predawn leaf water potential (MPa); PFD: photon flux density (μmol m-2 s-1); A: net CO 2 assimilation rate (μmol m-2 s-1); g w : leaf conductance to water vapour (mmol m-2 s-1); c i : intercellular concentration of CO 2 (μmol mol-1); Δw: leaf to air difference in vapour mole fraction; g L : specific hydraulic conductance from soil to leaves (mmol m-2 s-1 MPa-1); Fo, Fm and Fo', Fm': basal and maximal fluorescence after dark adaptation and 10 min at 220 μmol-2 s-1 , respectively; Fv/Fm: photochemical efficiency of PS II in dark-adapted leaves: ΔF/Fm' and Fv'/Fm': photochemical efficiency of PS II and of open PS II centres after 10 min at a given irradiance (220 or 800 μmol m-2 s-1); qp: photochemical quenching of fluorescence; A max : maximal rate of photosynthetic O 2 evolution under 5% CO 2 and 800 μmol mol-1 irradiance (μmol O 2 m-2 s-1), C: control treatment; PF: partially waterlogged treatment; F: completely waterlogged treatment.
Annals of Forest Science, 2013
& Context Waterlogging is predicted to become more common in boreal forests during winter and early spring with climate change. So far, little is known about the waterlogging tolerance of boreal tree species during their winter dormancy. & Aim The aim was to quantify the degree of waterlogging tolerance of 1-year-old dormant Norway spruce (Picea abies (L.) Karst.) seedlings. & Methods The seedlings were exposed to waterlogging in a growth chamber at temperature of 2°C for 4 weeks and then allowed to recover for 6 weeks during the growth stage. Shoot and root responses were monitored by physiological and growth measurements. & Results No effect was found in the seedling biomass, but root mortality increased slightly during the early growth stage following waterlogging. The water potential of the needles became less negative at the end of the waterlogging and the early growth stage. The ratio of apoplastic to symplastic electrical resistance (R e /R i ) of the needles was lower after waterlogging, indicating changes in the proportions of symplastic and apoplastic space. No differences were found between the treatments in the dark-acclimated chlorophyll fluorescence (F v /F m ) of the needles. Slightly greater accumulation of starch and temporary reductions of some mineral nutrients in needles were found after waterlogging. & Conclusions We conclude that in late winter and early spring, Norway spruce seedlings potentially tolerate short periods of waterlogging.
Tree Physiology, 1996
Aboveground xylem hydraulic conductance was determined in Scots pine (Pinus sylvestris L.) trees and stands from 7 to about 60 years of age. At the stand scale, leaf area index and net primary productivity (NPP, above- plus belowground) increased and reached a plateau at about 25-30 and 15-20 years, respectively; both parameters declined in mature stands. Stand hydraulic conductance followed a similar trend to NPP, with a maximum at about 15-20 years and a pronounced reduction in old stands. At the tree scale, annual biomass growth per unit of leaf area (growth efficiency) declined with tree age, whereas aboveground sapwood volume per unit leaf area, which is linearly related to maintenance respiration costs, steadily increased. Radiation interception per unit leaf area increased significantly with reduced leaf area index of mature stands, despite increased foliage clumping in the canopies of mature trees. Needle nutrient concentration did not change in the chronosequence. Tree hydraulic conductance per unit leaf area was strongly and positively correlated with growth efficiency. We discuss our findings in the context of growth reductions in mature and old trees, and suggest that increased hydraulic resistance and maintenance respiration costs may be the main causes of reduced carbon gain in mature and old trees.