Temperature affected the formation of arbuscular mycorrhizas and ectomycorrhizas in Populus angustifolia seedlings more than a mild drought

Arbuscular mycorrhizal (AM) plants and fungi associate with lower soil organic matter, higher pH, lower phosphorus and higher nitrogen than ectomycorrhizal (EM) ones. However, soil conditions correlate with climatic factors, and we suggest that temperature and humidity have also direct roles in the success of mycorrhiza types. The hypothesis here is that EM perform better at low temperatures than AM, and AM resist drought better than EM. Narrowleaf cottonwood (Populus angustifolia E. James) forms both AM and EM. We grew seedlings in soil at 14, 20 and 26 °C in factorial combinations with adequate watering and a cyclic mild drought for 4 and 7 weeks. As hypothesized, the percent of EM root tips was largest at 14 °C, while the proportional root length with AM was largest at the two higher temperatures. However, unlike expectations, drought increased EM formation slightly, while the AM colonization was lower in the dry treatment. Plant growth was reduced more by low temperature than drought. Root branching was more prominent at low temperature and root length and mass growth at higher temperatures. Soil nutrient availability did not provide a direct explanation to the results, as both soluble soil N and P were the same in 14 and 20 °C, while the change in mycorrhiza colonization took place between these temperatures. Differences in root morphology (root branching vs length) may affect the proportions of the mycorrhiza types at different temperature regimes. The most likely explanation to the differential colonization is that temperature affects AM and EM fungi in a different way. In nature, temperature and humidity regimes are tightly correlated, and temperature as such may be a stronger determinant for the success of mycorrhiza types than has been previously considered. The poorer performance of AM in low-temperature and drought conditions may reflect stress avoidance rather than stress tolerance by AM fungi.Peer reviewe

Morphological and ecophysiological root and leaf traits in ectomycorrhizal, arbuscular-mycorrhizal and non-mycorrhizal Alnus incana seedlings

Background and aims The aim was to assess possible benefits or drawbacks of arbuscular-mycorrhizal (AM) and ectomycorrhizal (EM) colonisation compared to no mycorrhizas (NM) in seedlings of the same host species. Eight broadleaf species were tested for mycorrhiza formation. Grey alder (Alnus incana) and four fungal species were selected for further experiments. Methods Grey alder seedlings were inoculated with AM fungi Rhizophagus intraradices and Glomus hoi or EM fungi Paxillus involutus plus an ascomycete isolated from Alnus roots or mock-inoculated (NM). Results EM formed in 70% of root tips and AM in 30% of root length. AM plants were smaller than EM and NM, but their specific root length (SRL) and specific leaf area (SLA) were highest. Net photosynthesis, stomatal conductance and shoot water potential did not differ between treatments. Foliar Ca, K, Mg, Mn, N, P and S concentrations (mg g−1) were highest in AM plants. However, total foliar contents (mg per plant) were lowest in AM plants, except for P, K and Zn. Conclusions The larger SRL and SLA suggest more efficient resource usage in AM plants, even though these were smaller than EM and NM plants. Grey alder is proposed as a new model species for comparisons between mycorrhiza types in cold climates.Peer reviewe

Soil frost affects stem diameter growth of Norway spruce with delay

Soil temperature and soil frost intensity are affected by the depth of insulating snow cover and the timing of snowmelt which are predicted to change by climate warming. This may increase tree growth if there is less soil freezing or decrease growth if there is no insulating snow cover, but frost temperatures still exist. Previously, we showed that the changes in soil frost by snow manipulations in a ~50-year-old stand of Norway spruce (Picea abies (L.) Karst.) in eastern Finland in two winters (2005/2006 and 2006/2007) led to short-term changes in physiology, morphology, and the growth of the shoots and roots. The treatments were: (i) control with natural insulating snow accumulation and melting; (ii) snow removal during winter; and (iii) snow removal in winter and insulation at the top of the forest floor in late winter to delay soil thawing. In this study, we examined lagged effects of those treatments by radial trunk increment cores during the nine-year recovery period after the termination of the treatments. Annual ring width index (AWI) was calculated for each year by normalization of the ring width in the respective year in proportion to the ring width in the last year (2005) before the treatments. No differences in AWI were found between the treatments before or during the snow manipulation period. However, differences started to appear one year after the treatments were finished, became significant four years later in 2011 and lasted for three years. The radial increment was lower in the treatment with snow removed than in the control and in the treatment with insulation to delay soil thawing, but there were no differences between the latter two treatments. The results indicate that a lack of snow cover may not only have short-term impacts but longer-lasting consequences on the radial growth of trees. The positive effects of prolonged growing season by the increasing summer temperatures on forest growth predicted for the boreal region may therefore not be fully realised due to the negative effects of decreased snow cover and increasing soil freezing

Early‐stage detection of root freezing injuries of Scots pine (Pinus sylvestris L.) seedlings by impedance loss factor and hydraulic conductance

The condition of the root system affects the quality of seedlings in forestry and horticulture. Previously, the electrical impedance loss factor (δ) and the reverse-flow hydraulic conductance (Kr) of the roots of Scots pine seedlings were found to increase when assessed a few days after frost damage. How these variables change with time after the root damage is unknown. We arranged an experiment with 1.5-year-old Scots pine seedlings exposed to −5°C or − 30°C, with the control seedlings kept at 3°C. Then, δ and Kr of roots were monitored for 5 weeks in favorable growing conditions. The properties of the roots were observed to be in a dynamic state after the damage. A significant difference in δ was found between the test temperatures −30°C versus −5°C and 3°C (p = 0.004 and p < 0.001, respectively). The clearest effect of freezing injuries on δ of roots was observed in the first measurement 1 week after the freezing test. The temperature significantly affected Kr, too, with a significant difference between the low-temperature treated plants −30°C versus −5°C and control (p < 0.001, respectively). The difference in Kr between −30°C and the other two temperatures increased with time and was the largest in the last samples, taken after 5 weeks. We conclude that the impedance loss factor may detect root damage if the measurements occur early enough after the damage, but a longer time difference (3–5 weeks) is needed according to the reverse-flow hydraulic conductance

Kekomuurahaiset ja puiden kasvu

Tieteen tor

Wood ants (<em>Formica rufa</em> group) in managed boreal forests: implications for soil properties and tree growth

Dissertation. University of Joensuu, Faculty of Forest Sciences. 200

Ants (Formica rufa group) in managed boreal forests: implications for soil properties and tree growth

Dissertation. University of Joensuu, Faculty of Forest Sciences. 200

Kekomuurahaisten (Formica rufa -ryhmä) vaikutus maaperän ominaisuuksiin ja puuston kasvuun hoidetuissa boreaalisissa metsissä

VäitöskirjaselosteSeloste väitöskirjasta: Kilpeläinen, J. 2008. Wood ants (Formica rufa group) in managed boreal forests: implications for soil properties and tree growth. Dissertationes Forestales 66