Abundancia de macroalgas

On the abundance of epiphytic green algae in relation to the

nitrogen concentrations of biomonitors and nitrogen deposition

in Finland

J. Poikolainena*, H. Lippo”, M. Hongistob, E. Kubin”, K. Mikkola’, M. Lindgrend

‘Muhos Research Station, Finnish Forest Research Institute, FIN-91500 Muhos, Finkmd

bFinnish Meteorological Institute, FIN-00101 Helsinki, Finland

CRovaniemi Research Station, Finnhh Forest Research Institute, FIN-96301 Rovaniemi, Finland

*Vantaa Research Centre, Finnish Forest Research Institute, FIN-013OI Vantaa, Finland

Received 27 March 1998; accepted 10 September 1998

Abstract

Green algae have become considerably more abundant in the years 19851995 in Finland and their distribution area has expanded

northwards. Green algae on conifers were most abundant in southern Finland where the nitrogen deposition is highest. Correlations

were observed between the abundance of green algae and a modelled nitrogen and sulphur deposition as well as the nitrogen

concentration of the biomonitors. The increased abundance of green algae in Finland may be caused by several concurrent changes

which have taken place in the environment and which have all promoted the occurrence of green algae. A slight rise in mean annual

temperature, the long-term stability of nitrogen deposition, and the clear fall in the amount of sulphur deposition have probably all

increased the growth and abundance of green algae. At a local level, the differences in microclimate have also effect on the

abundance of green algae and the microclimate varies, inter alia, by the nutrient-richness of the habitat, the predominant tree

species, stand age and stand density.

Keywords: Green algae; moss; lichen; pine bark; nitrogen deposition

Introduction

The deposition of nitrogen has increased in a large

part of Europe during the past few decades while at the

same time, that of sulphur has considerably diminished

(Barrett et al., 1995; Mylona, 1996). The emissions of

oxides of nitrogen in Finland have remained approximately

at the same annual level, 250 000 tonnes, and

those of ammonium, 50 000 tonnes, in the years 19&G

1995 (Ymptiristtikatsaus, 1995). Emissions of sulphur

dioxide have diminished during the same period from

about 300 000 tonnes to 100 000 tonnes. The total deposi-

* Corresponding author. Tel.: +358-B-531-2200, fax: +358-8-531-

2211; e-mail: jarmo.poikolainen@metla.fi

tion of oxidized nitrogen exceeds 3-4 kg (N) ha-’ year-’

and of the total reduced nitrogen 2-3 kg (N) ha-’ year-’ in

southern Finland (YmptiriWkatsaus, 1995; Hongisto,

1998). Both the oxidized and the reduced nitrogen deposition

decrease to the north and they are in northern

Finland correspondingly only l-l.5 kg (N) and 0.5-l kg

(N). Dry deposition varies 20-50% of total with the

seasons.

Atmospheric nitrogen in wet deposition is in nitrate

and ammonium form (NO,, NH,-) while in dry deposition

it is mainly in the form of gaseous nitric acid

(HNO,), ammonium (NH,) or nitrogen dioxide (NO,)

(Pitcairn et al., 1995; Hongisto, 1998). Nitrogen deposition

has a twofold ecological impact. On the one hand,

nitrogen causes acidification of the soil due to leaching of

base cations. On the other hand, it is a vital plant

86 J. Poikolainen et al. I Environmental Pollution 102, Sl (1998) 85-92

nutrient, which, when in excess, causes eutrophication. It

has been observed that increased deposition has caused

changes in vegetation, especially in areas of high

deposition in Central Europe, to the extent that

eutrophic plant species have increased at the expense of

oligotrophic species (e.g. Bobbink et al., 1992; Sutton et

al., 1993). If the vegetation is not able to bind free

nitrogen in the biological cycle, leaching will increase. In

areas where nitrogen deposition exceeds about lo-15 kg

N ha-* forested catchments show increased leaching of

nitrate (Grennfelt and Hultberg, 1986).

Research on nitrogen deposition and its impacts on

forest ecosystems has been relatively modest with respect

to the use of bioindicators when compared to the

research done on sulphur deposition. Part of the reason

probably lies in the fact that, due to it being an important

plant nutrient, it is more difficult to separate its effects

on vegetation than when dealing with sulphur. Green

algae have been used a little during the past few years as

bioindicators when examining nitrogen deposition

because it has been observed that they are sensitive to

changes in nitrogen deposition. Green algae are singlecelled

organisms, which take in their nutrients directly

from rain water and the air. Algae live in symbiosis with

lichens, among other things with Scoliciosporum chlorococcum.

Epiphyllic microbial cover often include also

various bacteria and fungi. The taxonomy of green algae

is still poorly known. Sochting (1997) has found that in

Denmark an algal crust on spruce needles consists of

among other things species belonging to the families

Apatococcus spp. and Desmococcus spp. The algae

require sufficient high temperature, high humidity and

suitable light for their growth. It would appear that

nitrogen is the most important factor restricting the

growth of green algae (Goransson, 1988). They occur in

abundance on trees and other suitable substrata in the

vicinity of various nitrogen sources, e.g. fertiliser factories,

fur farms, cattle farms, and in the urban areas (Ferm

et al., 1990, Goransson, 1990). Epiphyllic algae have

increased especially on Norway spruce (Picea abies)

needles in recent years in the southern parts of Fennoscandia

and in Central Europe (Goransson, 1988 and

1990; Peveling et al., 1992; Sochting et al., 1992;

Thomsen, 1992; Br&kenhielm and Liu Qinghong, 1995).

This study is a continuation of the epiphytic lichens

survey, carried out using the permanent sample plots of

the National Forest Inventory and to deposition mappings

using biomonitors (Kubin, 1990; Kuusinen et al.,

1990; Kubin and Lippo, 1996; Riihling et al., 1996;

Poikolainen et al., 1998). The present study reports on

the abundance of green algae on conifers during the

years 1985 and 1995 in Finland. The occurrence of green

algae has been compared to the nitrogen concentrations

of b&monitors, to the deposition of nitrogen and sulphur

obtained through modelling and to a few important

climate and site factors.

Materials and methods

The abundance of green algae was mapped by means of

nation-wide surveys of epiphytic lichens in 1985 and 1995.

These mappings were made on the network of 3009

permanent sample plots established in 1985-1986 in connection

with the 8th National Forest Inventory (Kuusinen

et al., 1990; Poikolainen et al., 1998). The networkconsists

of clusters of four 300 m2 circular sample plots in southern

and central Finland and clusters of tree plots in northern

Finland. The clusters are located in a 16x 16 km grid in the

south and 24x32 km in the north. The mapping of the

abundance of thirteen species or genera of epiphytic

lichens focused on conifers (Pinw sylvestris L., Picea abies

(L.), Karsten). The lichens were selected for inclusion in

the mapping on the basis of their presumed sensitivity to

sulphur dioxide. Scoliciosporum chlrorococcum + green

algae belonged to the group ‘tolerant species’. Green

algae live in symbiosis with lichens, usually Scoliciosporum

chlorococcum, and often include also various bacteria and

fungi. In this context, only the common name is used

because species were not identified in connection of the

mappings and their taxonomy is still poorly known

(Sochting et al., 1992). The abundance of lichens and

green algae were estimated using a scale O-3 on three

dominant trees closest to the plot midpoint between the

heights of 0.5-2.0 m around the tree both along the trunk

and among the branches (scale: 0 = no lichen and green

algae, 1 = sparse, 2 = fairly abundant; 3 = abundant).

When comparing the results of 1985 and 1995, only the

same trees were taken into consideration.

The same permanent sample plots were also used to

obtain biomonitor samples for deposition survey purposes

(Kubin, 1990; Riihling et al., 1996). The nitrogen

concentrations of the lichens (Hypogymniaphysodes) and

the pine (Pinus sylvestris L.) bark were determined from

the samples taken in 1985 and of the mosses (Hylocomium

splendens, Pleurozium schreberi) from the

samples taken in 1995. The samples were dried and

ground, and the nitrogen concentration was determined

using a slightly modified version of the micro-Kjeldahl

method (Kubin and Siira, 1980).

Nitrogen oxide, ammonium and sulphur depositions

in 1993 were computed by the HILATAR model developed

at the Finnish Meteorological Institute

...