Tapani Repo - Academia.edu (original) (raw)

Papers by Tapani Repo

EGU General Assembly Conference Abstracts, Apr 1, 2016

Metsätieteen aikakauskirja, 1970

Canadian Journal of Forest Research, Nov 1, 2019

Tree roots comprise a huge carbon pool. Their dynamics are driven by environmental factors and th... more Tree roots comprise a huge carbon pool. Their dynamics are driven by environmental factors and thereby affected by climate change. We studied the effects of soil temperature on root and shoot phenology and their linkages in Norway spruce (Picea abies). Saplings were grown in controlled-environment rooms for three simulated growing seasons (GS1, GS2, GS3). Soil temperature treatments 9, 13, 18 and 21°C were applied during GS2. Root growth was monitored with minirhizotrons. Root growth commenced in all treatments simultaneously. Temporal growth patterns of short and long roots were usually bimodal. Root growth was very low in the coldest treatment during GS2 but increased during GS3 as an after-effect. Short root growth also continued later after colder than warmer treatments during GS3. Reduced sink strength of roots and increased carbohydrate accumulation into needles at 9°C during GS2 probably enabled compensatory root growth under restored temperatures in GS3. Soil temperature did not affect shoot phenology, and root and shoot phenology varied between growing seasons; thus the linkage of root and shoot phenology was inconsistent. Root longevity was shorter and turnover rate higher in warmer than colder soil. This can further affect soil carbon dynamics and ecosystem carbon cycling in boreal forest ecosystems.

Journal of Geography & Natural Disasters, Dec 3, 2019

Tree Physiology, Mar 18, 2020

Future climate scenarios for the boreal zone project increasing temperatures and precipitation, a... more 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.

Silva Fennica, 2006

Two-year-old silver birch (Betula pendula) saplings were grown for a third growing season in cont... more Two-year-old silver birch (Betula pendula) saplings were grown for a third growing season in controlled-environment rooms (dasotrons) at three soil temperatures (5, 10, and 20°C). All trees grew the first flush of leaves, but the growth of the second flush was almost completely inhibited at the two lower temperatures. The dry weight of the second-flush leaves was 50 times larger at 20°C than at 5 and 10°C, with about 100 times more nitrogen. Root growth was less affected than shoot growth. Chlorophyll content, net assimilation rate and stomatal conductance were lower at low soil temperatures. The value of the cytoplasm resistance estimated from the electric impedance spectra was lower at 5°C than at 10 or 20°C. Leaf water potential was highest at the lowest soil temperature, and intercellular carbon dioxide concentration was only slightly lower in saplings growing in cooler soil. We conclude that the effect of long-term exposure to cold soil on net assimilation and growth was not caused by stomatal closure alone. It is likely to be additionally mediated by the limited nitrogen acquisition at the low soil temperatures, and perhaps additionally by some other factor. As the growth depression of aboveground parts in response to low soil temperature was more significant in silver birch than what has earlier been found in conifers, the relative changes in air and soil temperature may eventually determine whether birch will become more dominant in boreal forests with climate change.

Forest Ecology and Management, Feb 1, 2014

Frozen soil is predicted to change in the boreal areas with climate warming. We studied growth, l... more Frozen soil is predicted to change in the boreal areas with climate warming. We studied growth, longevity and mortality of fine roots at different levels of frozen soil in winter followed by a delayed soil thawing in spring in a 47-year-old stand of Picea abies (L. Karst.) in the boreal zone. The treatments, repeated over two winters, were: (i) natural insulating snow accumulation and melting (CTRL), (ii) snow removed during winter (OPEN), and (iii) as OPEN in winter but soil thaw delayed by insulation at the top of the forest floor (FROST). Short and long roots were monitored at different depths by minirhizotron imaging at onemonth intervals from May to October in the 2 years during and 2 years after the treatments, to assess standing length (SSL), production volume (SPV) and mortality. A survival function estimate was calculated according to the nonparametric maximum likelihood estimate for interval censored data, and the mean and median root longevities were calculated as with a Kaplan-Meier estimate. CTRL and OPEN did not differ for SSL and SPV but they differed in FROST where compensatory growth occurred in the follow-up seasons. The mean longevity ranged from 276 to 305 days for short roots and from 425 to 464 days for long roots, being higher in OPEN than CTRL and FROST, and higher in the deeper soil layers than near the soil surface. The mean and median longevities were largely the same for short roots but the means were 80-100 days higher for long roots. We conclude that the winters with deep soil freezing are not detrimental for fine roots of Norway spruce, insofar as soil thawing will not prolong the growing season. The longer lifetime in OPEN suggests declining carbon flux into the soil following winters with deeply frozen soil.

Tree Physiology, Aug 1, 2008

In boreal regions, soil can remain frozen after the start of the growing season. We compared rela... more In boreal regions, soil can remain frozen after the start of the growing season. We compared relationships between root characteristics and water relations in Scots pine (Pinus sylvestris L.) saplings subjected to soil frost treatments before and during the first week of the growing period in a controlled environment experiment. Delayed soil thawing delayed the onset of sap flow or totally blocked it if soil thawing lagged the start of the growing period by 7 days. This effect was reflected in the electrical impedance of needles and trunks and in the relative electrolyte leakage of needles. Prolonged soil frost reduced or completely inhibited root growth. In unfrozen soil, limited trunk sap flow was observed despite unfavorable aboveground growing conditions (low temperature, low irradiance, short photoperiod). Following the earliest soil thaw, sap flow varied during the growing season, depending on light and temperature conditions, phenological stage of the plant and the amount of live needles in the canopy. The results suggest that delayed soil thawing can reduce tree growth, and if prolonged, it can be lethal.

Tree Physiology, Aug 1, 2005

Effects of the timing of soil thawing in the spring on Scots pine (Pinus sylvestris L.) were stud... more Effects of the timing of soil thawing in the spring on Scots pine (Pinus sylvestris L.) were studied under controlled laboratory conditions. Sixteen 6-year-old saplings were lifted from the field, replanted in containers and placed in four treatments in controlled environment (CE) chambers with four replicate saplings per chamber. The saplings were held in the CE chambers during one simulated winter and one simulated growing season. The soil was frozen to-2°C during a second simulated winter in the CE chambers, and the soil thawing treatments began at the end of the second simulated winter. Soil thawing began at various times before (no delay in thawing) and after (delay in thawing) chamber air conditions were changed from simulated winter to simulated summer. Delayed soil thawing subjected saplings to stress, with the severity of stress depending on the length of the delay in thawing. If there was no delay or only a short delay in soil thawing, stress was minor and reversible. A 2-week delay in soil thawing led to death of the saplings. Stress was apparent as decreases in the variable to maximal chlorophyll fluorescence ratio (F v /F m), chlorophyll a/b ratio and needle water potential. In needles of stressed saplings, apoplastic electrical resistance first decreased and then increased and there were anomalies in the electrical impedance spectra of the stems. Stress from the soil thawing treatments affected both root and shoot growth.

Canadian Journal of Forest Research, Dec 1, 2016

In the future management and sustainable use of boreal forests it is crucial to consider the rate... more 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-yearold Scots pine (Pinus sylvestris L.) seedlings to a five-week waterlogging (WL) 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 respirationwere observed after three 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 decrease in sap-flow. We conclude that through negative feedback on transpiration and net photosynthesis, WL during the growing season is harmful for Scots pine, leading to potential growth losses or even dying of trees within a few weeks of WL.

To avoid the surrounding pollination, seed orchards of Finnish plus trees have been established i... more To avoid the surrounding pollination, seed orchards of Finnish plus trees have been established in Ukraine, i.e. far from their natural distribution. However, it is not known whether the pollination site affects the frost hardiness (FH) of the progenies, and therefore their use in forest regeneration in Finland. Using whole-plant freezing tests, we examined the FH of plus-tree seed orchard progenies in Finland and Ukraine, with three lots of seeds from each origin, twice during cold acclimation in controlled conditions. The FH of needles, as assessed immediately after the freezing tests, was higher in the Finnish than Ukrainian seed orchard progenies. The variation in the FH of needles was high among the progenies, ranging from − 44°C to − 79°C by relative electrolyte leakage (REL), and from − 29°C to − 46°C by chlorophyll fluorescence (CF). When the FH was assessed according to the growth of shoots and roots after growing the seedlings for three weeks in the greenhouse the differen...