Effect of waterlogging on boreal forest tree seedlings during dormancy and early growing season

Abstract

More precipitation in the form of rain in winter together with deteriorated ditch networks may expose drained peatland forestry to winter or spring waterlogging in boreal forests. The response of main boreal forest species on soil waterlogging is important for predicting forest productivity and justifying the demand for ditch network maintenance. In this study, the aim was to find out the physiological and growth responses of 1-year-old Norway spruce (Picea abies (L.) Karst.), silver birch (Betula pendula Roth) and pubescent birch (Betula pubescens Ehrh.) seedlings subjected to one-month waterlogging at the end of the dormancy phase, and to find out the morphology, physiology and growth of silver birch and pubescent birch seedlings subjected to one-month waterlogging at the beginning of the growing season.Two experiments were carried out in growth chambers. In experiment 1, Norway spruce seedlings were subjected to either no waterlogging or waterlogging for one month at 2 o C, after which a six-week follow-up growing season allowed the seedlings to recover. In experiment 2, silver birch and pubescent birch seedlings went through a four-week dormancy (weeks 1-4), a four-week early growing season (weeks 5-8), and a four-week late growing season (weeks 9-12). The treatments were 1) no waterlogging throughout the experiment (NW); 2) four-week waterlogging during dormancy (Dormancy waterlogging, DW); 3) four-week waterlogging during the early growing season (Growth waterlogging, GW); and 4) four-week dormancy waterlogging followed by four-week growth waterlogging during the early growing season (DWGW).Dormancy waterlogging reduced root volume and increased root mortality, but did not affect dark-acclimated chlorophyll fluorescence (F v /F m ) or the biomass of leaves, stems and roots in Norway spruce. Root biomass and root hydraulic conductance (K r ) of silver birch was reduced but aboveground organs were not affected by dormancy waterlogging. On the contrary, in pubescent birch root morphology, biomass and K r were not affected, but gas exchange was reduced by dormancy waterlogging. However, the biomass of leaves and stems was not negatively affected in pubescent birch. In conclusion, these tree species can tolerate a one-month winter waterlogging well.Growth waterlogging led to the reduction of stomatal conductance (g s ), and thus the reduction of light-saturated photosynthesis rate (A max ) in both birch species, although recovery was seen during the follow-up growing season. It also led to lower leaf area in both birch species. Growth waterlogging led also to decreased the K, Ca, Mg, Mn and B contents of leaves in silver birch, whereas in pubescent birch only Ca and Mg contents were decreased. In pubescent birch, fine cluster roots, the incidence of non-glandular trichomes, and stem lenticels were increased by growth waterlogging. However, silver birch did not show such acclimation to waterlogging. In conclusion, growth waterlogging caused more negative effects to both birch species than dormancy waterl...